UC-NRLF 


1869 


TIIK 


EARLY  STAGES  OE  TEREIJRATUIJNA  SEPTENTRIONALIS. 


BY   KDWARD  S.   AIORSK.   Pii.I)., 

<!!•     COMI'AKATIVI'.     ANATuSlY      AMI    /OOI.1H.V     IN     1«IWHO1.\     I  Ol.l.HI :  K. 


From  tlie  Memoirs  of  the  Boston  Society  of   Natural  History,   Vol.  II. 


ON    THE 


EARLY  STAGES  OF  TEKEBKATULINA  SEPTENTRIONALIS. 


BY  EDWARD  S.  MORSE,  PH.D., 

PBOFB880R   OK    COMPARATIVE    ANATOMY    AN11    ZOOmGY    IN    BOWDOIN    C'OLLEOB. 


ifa»  Lib, 


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BIOLOGY 

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II.     Ox   THE    EARLY    STAGES    OF   TEREBRATULINA    SEPTENTRIONALIS    (Couthouy.) 

By  EDWARD  S.  MORSE. 

Read  October  20th,  1869. 

JL  HERE  is  hardly  a  group  among  the  lower  animals  (if  we  consider  the  relatively  small 
number  of  species  represented  by  it)  that  has  attracted  the  attention  of  so  many  natural- 
ists as  the  Brachiopoda.  The  names  of  Cuvier,  Owen,  Vogt,  Huxley,  Hancock,  Gratiolet, 
Lacaze-Duthiers,  Bouchard-Chantereaux,  Miiller,  Davidson,  Carpenter,  King,  d'Orbigny 
and  a  host  of  others,  are  sufficient  evidence  of  the  interest  felt  in  a  group  whose  organ- 
ization links  them  so  closely  with  the  past. 

The  desire  to  interpret  through  a  knowledge  of  its  living  forms  the  many  species  which 
are  now  extinct,  as  well  as  to  ascertain  the  relations  it  bears  to  the  other  divisions  of  the 
animal  kingdom ;  the  contemplation  of  a  group  whose  maximum  development  in  genera 
and  species  was  attained  in  the  Devonian  age,  though  its  representatives  are  strewn 
through  the  rocks  of  all  ages  since  the  dawn  of  life  upon  the  globe ;  the  remarkable  fact 
that  among  the  earliest  forms  of  organic  life  known,  are  genera  whose  species  can  hardly 
be  distinguished  from  present  existing  forms,  all  explain  the  attractions  its  study  has 
afforded  alike  to  Zoologists  and  Paleontologists. 

The  splendid  memoirs  upon  the  Brachiopoda  by  some  of  the  authors  just  mentioned, 
more  particularly  those  of  Albany  Hancock,1  Vogt  and  Gratiolet,  offer  but  little 
encouragement  to  one  entering  the  field  with  the  expectation  of  gleaning  anything  new. 
While,  however,  the  anatomy  and  histology  of  the  adult  animal  of  several  species  has 
been  carefully  worked  up,  little  or  nothing  has  been  done  toward  elucidating  the  embryol- 
ogy, or  the  early  stages  of  the  class.  Fritz  Miiller2  has  given  in  a  short  note  a  descrip- 
tion and  two  figures  of  what  he  considers  an  early  stage  of  a  species  of  Distinct,  and 
Lacaze-Duthiers 3  has  made  some  extremely  interesting  observations  on  the  embryo  of 
Thecidium.  Aside  from  these  two  papers,  we  know  of  nothing  whatsoever  relating  either 
to  the  embryology  or  the  early  stages  of  the  Brachiopoda.  The  importance  and  neces- 
sity of  some  information  regarding  the  embryology  of  these  animals  has  been  urged  by 
many  writers,  for  it  was  believed  that  the  relations  between  them  and  the  Polyzoa,  as 
urged  by  Agassiz,  Milne  Edwards,  Huxley,  Hancock,  Dana  and  others,  would  be  verified, 
when  the  development  of  Brachiopoda  was  known.  In  this  path  of  inquiry  the  investi- 
gator will  find  an  open  field. 

For  a  long  time  I  have  been  interested  in  the  relations  of  the  class  under  consideration, 

1  On  the  organization  of  the  Brachiopoda.     Philosophical  2  Archiv  fur  Anatomie  Reichart  et    Du    Bois  Raymond, 

Transactions    of  the  Royal    Society,    London,    1858,    vol.       1860,  p.  72. 

CXLVIII,  part  2.  »  Histoire  de  la  Thecidie.     Annales  des  Sciences  Nat.     4th 

series,  tome  XV,  p.  262. 

JJKMOIHR   HOST.   SOC.   NAT.   H1RT.      VOL.   II.  8 


399367 


30  EARLY    STAGES    OF    TEREBRATULINA. 

ft 

and  in  an  early  paper  entitled  "  Haemal  and  Neural  regions  of  Brachiopoda,"  1  and  later, 
in  a  paper  on  the  "  Classification  of  Mollusca,  based  on  the  principle  of  Cephalization,"  2 
urged  the  intimate  relations  existing  between  the  Brachiopoda  and  Polyzoa.  With 
the  hopes  of  learning  something  about  the  early  stages  of  one  of  our  native  species  of 
Brachiopoda,  I  visited  Eastport,  Maine,  in  the  early  part  of  June,  1869,  and  this  com- 
munication embraces  a  summary  of  the  incomplete  observations  there  made  ;  incomplete, 
as  I  was  unable  to  secure  any  data  on  the  embryology  of  the  species.  At  the  outset  my 
microscope  proved  altogether  inadequate  to  the  work  before  me,  though  the  minute  size  of 
the  objects  examined,  coupled  with  the  complicated  texture  of  the  shell  through  which 
the  soft  parts  had  to  be  observed,  rendered  the  work,  at  the  best,  laborious  and  difficult. 
In  every  case,  however,  the  figures  given  in  the  accompanying  plates  are  correct  tran- 
scripts of  the  drawings  made  from  the  animal :  in  no  instance  is  there  given  any  combina- 
tion of  several  unfinished  sketches  to  make  a  more  intelligible,  or  perfect  whole.  This 
will  explain  the  absence  of  detail  and  completeness  in  many  of  the  figures  presented ;  at 
the  same  time  it  is  believed  that  the  outlines  will  be  more  valuable  from  the  fact  that  they 
are  not  schematic  or  composite. 

For  a  clear  exposition  of  the  organization  of  the  Brachiopoda,  I  would  refer  to  the 
exhaustive  memoir  of  Albany  Hancock  above  referred  to,  a  memoir  which  justly  mer- 
ited the  honor  conferred  upon  him  in  the  award  of  the  Royal  medal. 

On  the  early  stages  of  Terebratulina  septentrionalis  Couthouy?  The  specimens  upon 
which  the  following  examinations  were  made,  were  dredged  in  fifteen  fathoms  of  water  in 
the  harbor  of  Eastport,  Maine,  in  the  first  week  of  June,  1869.  The  species  occur  in 
great  numbers,  at  various  depths,  and  have  also  been  collected  at  low  tide  mark,  by  Dr. 
Stimpson  and  Prof.  Verrill.  The  specimens  were  found  attached  to  stones  brought  up  in 
the  dredge,  and  also  adhering  to  the  lower  valve  of  adult  individuals,  generally  near  the 
peduncle.  An  examination  of  adult  individuals  showed  that  while  the  ovaries  in  some 
specimens  were  empty,  in  others  they  were  fully  charged ;  in  some  the  ovaries  would  be 
partially  empty,  in  others  the  ovaries  of  one  side  would  be  nearly  empty,  while  those  of 
the  other  side  would  be  quite  full.  Specimens  collected  by  Prof.  Verrill  in  August,  were 
found  with  eggs ;  and  eggs  were  also  noticed  in  specimens  less  than  three  sixteenths  of  an 
inch  in  length.  The  eggs,  fig.  1,  were  generally  kidney-shaped,  though  very  irregular 
as  to  form  and  size ;  they  were  spermaceti  white  in  color,  and  opaque,  though  having  a 
central  area,  translucent,  and  apparently  depressed.  In  general  outline  they  suggest  the 
kidney-shaped  eggs  of  Fredericella.  No  intermediate  stage  was  observed  between  the 
ovarian  egg  and  the  stage  represented  in  fig.  2.  This  form  recalled  the  general  propor- 
tions of  Argiope  and  Megerlia,  in  being  transversely  oval,  in  having  the  hinge  margin 
wide  and  straight,  and  in  the  presence  of  a  proportionately  wide  foramen.  This  stage  was 
exceedingly  minute,  and  only  two  individuals  were  discovered  ;  they  were  attached  to  the 
rock,  resting  on  the  broad  hinge  area  ;  nothing  could  be  traced  of  the  structure,  except  an 
appearance  of  granular  contents,  as  indicated  in  the  figure  ;  the  shell  showed  nothing  of 

1  Proceedings  Boston  Society  Natural  History,  vol.  IX.  can  Naturalist,  Sept.  no.,  vol.  Ill,  1869.  Since  reprinted  in 

1862.  American  Journal  of  Science  and  Arts  for  Jan.,  1870. 

'Proceedings  Essex  Institute,  Salem,  vol.  IX,  part  6  The  general  results  were  communicated  at  the  18tli  An- 
1865.  Also  reprinted  in  American  Journal  Science  and  nual  Meeting  of  the  American  Association  for  the  Advance- 
Arts,  vol.  XLII,  no.  124.  1866.  ment  of  Science,  Aug.,  1869. 

'  A  brief  resume  of  this  paper  was  published  in  the  Amer- 


EARLY   STAGES   OP   TEREBRATULINA.  31 

the  scale-like  structure  so  characteristic  in  later  stages.  Between  this  stage  and  the  next, 
fig.  3,  the  shell  rapidly  elongates,  while  the  hinge  margin  remains  nearly  the  same  in 
width;  this  is  also  shown  in  the  concentric  lines  of  growth  seen  faintly  on  the  surface, 
indicating  a  rapid  increase  in  the  length  of  the  shell,  while  no  corresponding  increase 
takes  place  in  the  widening  of  the  hinge  margin.  The  peduncle  is  longer  than  the  shell, 
having  distinct  walls  apparently  enclosing  a  clear  interspace,  the  end  slightly  dilating  and 
forming  a  pear-shaped  adhering  disk.  The  structure  of  the  shell,  of  which  more  will  be 
said  in  subsequent  pages,  showed  clearly  the  scale-like  structure,  with  the  cascal  tubules 
of  the  pallial  lobes  perforating  it.  The  anterior  margin  of  the  pallial  lobes  gave  rise  to 
seven  setoe  of  variable  lengths,  all  of  them  projecting  forward.  These  setse,  in  nearly  all 
instances,  were  clothed  with  desmids,  and  were  probably  available  in  attracting  sustenance 
to  the  animal ;  they  resembled  in  structure  the  setse  of  the  adult,  as  figured  by  Hancock, 
and  the  longest  of  them  was  as  long  as  the  shell.  The  future  position  of  the  calcareous 
loop  was  indicated  by  a  strongly  arched  process  midway  the  length  of  the  shell,  from 
which  sprang  six  short  and  stout  cirri,  all  of  them  curving  towards  the  mouth,  which 
occupied  the  centre  of  the  base  from  which  the  cirri  sprang.  The  digestive  sac  hung 
from  the  mouth,  and  was  twice  as  long  as  broad,  having  a  strong  constriction  in  the  cen- 
tre, forming  two  chambers,  the  lowermost  one  being  globular  in  shape,  and  having  its 
walls  colored  a  light  reddish-brown,  this  colored  portion  evidently  indicating  hepatic  cells. 
The  cavity  next  the  mouth  indicates  the  stomach,  while  the  lowermost  cavity  indicates 
the  future  intestine,  or  cul  de  sac.  The  cirri  moved  frequently,  and  in  various  directions, 
though  generally  performing  a  grasping  motion,  as  if  securing  some  bit  of  food,  imitating 
precisely  the  movement  of  the  cirri  in  Polyzoa,  and  this  resemblance  was  more  complete 
from  the  fact  that  the  tentacles  were  densely  clothed  with  cilia  (fig.  4),  and  their  move- 
ments caused  visible  currents  in  the  water.  The  two  cavities  of  the  digestive  sac  were  also 
ciliated,  and  little  pellets  of  food  were  seen  rapidly  circulating  back  and  forth  from  one 
cavity  to  the  other.  The  cavities  were  alternately  dilating  and  contracting,  and  assumed 
the  forms  represented  in  figs.  5j  6  and  7.  At  this  stage  the  lower  cavity  of  the  digestive 
sac  was  diverted  to  the  larger  valve,  as  represented  in  fig.  4. 

In  this  stage,  and  several  succeeding  stages,  the  outline  of  the  shell  is  remarkably  like  that 
of  Linr/ula,  and  this  resemblance  is  more  striking  from  the  proportionately  long  peduncle. 

In  another  stage,  numerous  irregular  shaped  calcareous  spiculaa  lined  the  outer  margin 
of  the  cirri,  while  the  future  position  of  the  calcareous  loop,  or  crura,  was  indicated  by  a 
row  of  irregular  shaped  spiculse,  the  correct  forms  of  which  are  given  in  fig.  15. 

Fig.  16  represents  portions  of  two  cirri  more  highly  magnified,  in  which  correct  out- 
lines are  given  of  the  spiculte.  It  is  to  the  presence  of  these  calcareous  particles  that  we 
must  account  for  a  certain  rigidity  noticed  in  the  texture  of  the  cirri.  In  these  slightly 
advanced  stages,  the  peduncle  becomes  much  shorter  in  proportion  to  the  length  of  the 
shell,  though  the  shell  presents  the  same  lingula-like  form,  differing,  however,  from  Lingula 
in  the  much  greater  length  of  the  neural  valve,  which  is  always  perforated  and  rostrated 
from  the  outset. 

In  all  these  stages  the  peduncle  has  very  slight  adhesion  to  the  rock,  or  whatever  sub- 
stance it  may  be  attached  to,  in  this  respect  differing  greatly  from  the  adult,  which 
often  requires  great  force  to  detach  it,  frequently  leaving  the  peduncle  separated 
from  the  body,  and  adhering  to  the  rock. 


32  EARLY  STAGES  OF  TEREBRATULINA. 

In  figs.  8  and  9  are  given  side  views  of  the  shell  at  this  period.  The  flatness  of  the 
valves  will  be  observed,  again  resembling  Lingula  in  this  respect ;  the  under  valve  is 
much  flatter  than  the  upper  one.  I  was  fortunate  in  observing  an  individual  at  this  age 
in  motion.  The  animal  whirled  quickly  on  its  peduncle ;  when  at  rest  the  shells  were 
always  closed,  and  rested  on  the  rock ;  from  this  position  it  turned  slowly  more  than  half 
way  round,  raising  the  body  at  the  same  time  almost  erect ;  this  movement  being  com- 
pleted, the  valves  would  very  slowly  open,  and  the  cirri  expand  as  if  to  perform  a 
grasping  motion ;  in  no  case,  however,  were  they  projected  beyond  the  margin  of  the 
valves.  The  cilia  lining  the  cirri  produced  gentle  currents  in  the  water.  In  this  position, 
with  the  valves  widely  open  and  eirri  expanded,  the  animal  would  remain  motionless  for 
twenty  or  thirty  seconds,  and  then,  with  an  abrupt  closing  of  the  valves,  suddenly  assume 
its  first  position.  These  two  positions  are  represented  in  fig.  10,  where  the  animal  is  seen 
from  the  side,  and  in  fig.  11,  where  it  is  seen  from  above.  The  outline  marked  A  repre- 
sents the  shells  closed  and  at  rest,  while  B  represents  the  shells  open ;  the  line  of  arrows 
indicates  the  direction  of  the  rotatory  movement. 

In  watching  these  motions  for  a  long  time,  one  could  not  help  being  impressed  with  the 
fact  that  caution  was  evidently  indicated  in  the  slow  and  careful  movements  made  in  ele- 
vating and  opening  the  shell,  while  the  prompt  closing  of  the  valves,  and  the  alert  man- 
ner in  which  the  animal  regained  its  first  position  seemed  to  show  that  food  had  been 
secured,  and  further  caution  was  unnecessary. 

In  another  stage,  fig.  12,  the  tentacles  were  seen  of  various  lengths,  some  of  them  just 
budding  from  the  lophophore.  A  fold  upon  each  side  of  the  stomach  was  first  noticed ; 
these  folds  are  the  first  appearance  of  the  liver.  At  this  time  the  hepatic  folds  expand 
and  contract  independently  of  each  other  (fig.  14). 

In  fig.  13  another  view  of  the  same  individual  is  given,  where  the  upper  portion  of  the 
digestive  sac,  or  that  portion  which  answers  to  the  oesophagus  and  stomach,  is  in  a  con- 
tracted state,  while  the  lower  portion  is  widely  expanded.  A  peculiar  constriction 
appears  at  times  between  the  two  chambers  of  the  digestive  sac,  which  recalls  the  cardiac 
or  oesophageal  valve,  as  seen  in  the  Phylactolaematous  Polyzoa ;  it  has  no  coniform  projec- 
tion into  the  stomach,  and  really  appears  more  distinctly  as  an  annular  dilatation.  All 
traces  of  it  disappeared  during  certain  expansions  and  contractions  of  the  gastric  walls. 
All  portions  of  the  sac  and  the  lateral  folds  were  strongly  ciliated,  and  the  food,  now 
gathered  into  round  pellets,  and  again  scattered  in  granules,  was  violently  impelled  back 
and  forth. 

In  fig.  4,  the  cirri  are  shown,  clothed  with  cilia ;  in  fig.  12  the  cirri  are  shown  plain, 
while  the  cilia  are  shown  lining  the  digestive  sac.  In  fig.  15  only  the  calcareous  spiculse 
are  shown ;  but  in  all  these  cases  each  possesses  the  characters  of  the  others,  which  for 
clearness  are  shown  singly. 

Fig.  17  exhibits  the  only  example  where  the  soft  parts  are  drawn  from  an  alcoholic 
specimen.  In  this  example  is  first  seen  a  set  of  muscles,  rendered  visible  by  their  con- 
traction in  alcohol,  and  consequent  greater  density.  They  are  probably  the  divaricator 
muscles,  though  somewhat  in  advance  of  what  their  position  would  be  in  the  adult  state. 

Owing  to  the  contraction  of  the  digestive  sac,  its  diverticular  cavities  are  sharply  de- 
fined, and  the  globular  appearance  of  the  lower  cavity  is  marked.  In  another  alcoholic 
specimen  of  the  same  age,  a  band,  evidently  one  of  the  lateral  gastro-parietal  bands,  was 


EARLY    STAGES    OF   TEREBRATITLINA.  33 

made  out.     As  this  could  not  be  verified  in  other  specimens  of  the  same  age,  the  figure  is 


not  given. 


A  still  more  advanced  stage  is  shown  in  fig.  21.  The  shell  is  now  becoming  propor- 
tionately broader,  and  the  cirri  increase  in  number,  though  still  forming  a  simple  circle 
around  the  mouth.  The  crura  have  also  begun  to  form. 

In  fig.  22  a  considerably  more  advanced  state  is  shown.  The  valves  have  been  forcibly 
separated,  and  the  smaller  one  is  thrown  back.  The  cirri  are  more  numerous,  numbering 
thirty-one ;  two  of  them  are  seen  encroaching  upon  the  circular  lophophore,  and  at  this 
stage  the  lophophore  has  begun  to  assume  its  hippocrepian  character. 

The  crura  (cr)  are  plainly  seen  supporting  the  crown  of  cirri,  and  the  liver  already 
shows  the  first  indications  of  its  differentiations  into  the  peculiar  caecal  ramifications  which 
become  so  numerous  in  the  adult ;  and  at  this  stage  is  seen  the  division  of  each  lateral 
portion  of  the  liver  into  a  dorsal  and  ventral  lobe ;  a  lateral  lobe  is  shown  in  fig.  23. 
It  will  be  seen  that  the  liver  is  divided  into  a  series  of  caeca,  though  these  are  united. 

The  divaricators  (d)  are  completely  formed,  and  between  these  two  muscles  is  seen  the 
lengthened  intestine  (i),  the  blind  extremity  of  which  is  held  firmly  to  the  shell  by  a 
membrane,  called  by  Hancock  the  ventral  mesentery. 

The  appearance  of  the  shell  at  this  stage  is  represented  in  fig.  26.  Radiating  ribs,  to 
the  number  of  fifteen,  ornament  the  shell.  It  will  be  seen  by  this  figure,  that  the  setae 
correspond  in  growth  and  position  to  the  radiating  furrows,  and  this  observation  is  also 
made  by  Hancock  in  his  examination  of  the  adult.  A  well  defined  concentric  line  seems 
to  indicate  the  earlier  lingula-shaped  shell,  and  though  no  ribs  appear  in  the  earlier  stages, 
they  are  defined  upon  this  area  afterward,  and  it  would  appear  from  this  that  the  ribs  are 
formed  on  the  inner  surface,  and  that  the  setae  direct  and  induce  the  furrow.  The  lobes 
of  the  liver  (?),  and  the  peduncle  (p)  and  peduncular  capsule,  are  shown  in  this  figure. 

In  fig.  24  a  stage  still  more  advanced  is  given ;  the  valves  are  thrown  back,  disclosing 
the  stomach  and  intestine  suspended  from  the  calcareous  loop.  The  crura  (cr)  are  well 
defined,  and  the  ventral  mesentery  (vm)  is  more  distinctly  seen  in  this  figure.  Two 
lateral  bands  are  seen  holding  the  stomach  in  position ;  and  these  appear  to  be  attached 
to  the  crura,  though  they  probably  pass  by  them,  and  become  attached  to  the  haemal 
valve.  These  are  the  lateral  gastro-parietal  bands  first  described  by  Huxley. 

The  walls  of  the  blind  intestine  are  yet  light  brownish  in  color,  as  in  the  Phylactolae- 
mata,  and,  as  before  remarked,  are  hepatic.  A  kidney-shaped  area  is  faintly  defined  on 
the  neural  valve.  A  portion  of  this  outline  indicates  the  point  of  attachment  of  the 
perivisceral  wall. 

In  fig.  24a  an  enlarged  view  of  the  digestive  sac  and  adjacent  parts  of  fig.  24  is  shown. 
The  liver  in  this  stage  communicates  with  the  stomach  by  large  openings  on  each  side,  and 
fine  granules  were  seen  rapidly  circulating  to  and  fro,  from  the  liver  to  the  stomach. 
The  ftcces,  rolled  into  a  spiral  and  pyriform  shape,  were  constantly  in  motion  by  the  action 
of  the  cilia  lining  the  stomach.  This  mass  was  frequently  urged  toward  the  mouth 
before  it  was  finally  discharged.  The  passage  of  the  faeces  through  the  mouth  was  repeat- 
edly witnessed  ;  though  after  the  careful  investigations  of  Huxley,  Hancock,  Lacaze- 
Duthiers  and  Gratiolet,  no  further  proof  is  needed  of  the  absence  of  an  anal  outlet  to  the 
intestine  of  this,  and  allied  species. 

The  experiments  of  Mr.  Hancock,  such  as  bursting  the  intestines  under  a  compressor, 


MKM01U8  BO8T.  8OC.    NAT.    HIST.      VOL.  II. 


34  EARLY    STAGES    OF   TEREBRATULINA. 

were  performed  on  many  living  adult  specimens,  yet  in  no  case  was  the  slightest  evidence 
of  an  anal  outlet  observed. 

Fig.  25  represents  a  stage  but  slightly  advanced  from  fig.  24.  The  cirri  are  more  nu- 
merous, but  still  spring  from  a  circular  lophophore. 

Fig.  27,  plate  n,  represents  a  considerably  advanced  stage,  in  which  the  lophophore, 
before  circular,  has  rapidly  assumed  its  hippocrepian  character ;  rapidly,  —  since  forms 
nearly  of  the  same  size  show  no  marked  indications  of  change,  for  in  one  example  we 
may  have  a  circular  lophophore,  or  one  showing  but  slight  indentation,  while  in  another 
example,  hardly  differing  in  size,  we  have  the  lateral  processes  well  advanced  in  develop- 
ment. It  is  possible  that  we  may  have  here  a  feature  observed  by  Fritz  Miiller  in 
the  young  Discina  described  by  him ;  he  mentions  the  remarkable  fact  of  having  re- 
peatedly captured  free  swimming  young  which  had  evidently  advanced  further  in  their 
development  than  the  oldest  of  those  which  had  already  fixed  themselves.  It  will  be 
noticed  that  in  this  stage  (fig.  27)  the  cirri  stand  erect  upon  the  arms,  that  is  pointing 
towards  the  anterior  margin  of  the  shell,  and  that  the  arms  are  not  deflected.  This 
stage  of  the  lophophore  vividly  recalls  the  hippocrepian  forms  among  the  Polyzoa,  such 
as  Plumatella,  Cristatella,  Lophopus  and  others. 

The  liver  now  shows  its  adult  characters  in  having  its  ramified  caeca  separated,  and  not 
adhering  by  their  walls  in  one  mass.  In  this  early  condition  it  resembles  the  liver  of 
Thecidium,  as  described  and  figured  by  Lacaze-Duthiers. 

Fig.  28  represents  a  stage  where  the  arms  become  deflected  ;  as  yet  no  central  process 
of  the  lophophore  is  developed ;  the  mouth  is  very  large,  and  that  margin  of  it  not  bear- 
ing cirri  is  very  pliant  in  its  movements. 

In  the  next  stage  (fig.  29)  the  arms  are  more  deflected  and  make  a  sharper  curve  in 
their  approach  together,  and  the  central  process  of  the  lophophore  is  indicated  by  that 
portion  forming  the  base  of  the  inner  curve,  developing  into  two  prominences.  The  free 
lip  is  seen  in  irregular  curves,  and  these  changed  with  every  movement  of  the  parts. 

Fig.  30  represents  a  slightly  more  advanced  stage,  where  the  central  processes  of  the 
lophophore  are  more  developed.  The  free  lip  is  here  seen  thrown  broadly  back,  disclosing 
a  capacious  mouth,  within  which  are  seen  two  blunt  projections,  though  in  another  view  of 
the  mouth  (fig.  31)  only  one  projection  was  observed.  The  free  lip  seemed  to  perform 
all  the  functions  pertaining  to  the  epistome  in  the  higher  Polyzoa,  and  we  find  it  on  the 
inner  bend  of  the  arms,  as  in  the  Polyzoa,  though  not  occupying  the  same  homological 
position  in  regard  to  the  flexture  of  the  intestine.  It  will  be  noticed  that  in  all  these  stages 
the  cirri  are  comparatively  thick. 

In  the  stage  represented  by  fig.  32,  the  cirri  become  more  attenuated  and  increase  rap- 
idly in  number ;  the  central  process  is  more  advanced,  though  not  yet  thrown  into  a 
vertical  spiral,  as  in  the  adult,  and  the  mouth  has  lost  the  broad  reflected  character  of 
the  lip,  which  it  possessed  in  the  earlier  stages,  though  the  free  lip  has  yet  considerable 
pliancy,  as  seen  in  figs.  33  and  34,  where  other  views  of  the  same  mouth  are  presented. 
For  the  first  time  now  appears  another  adult  character,  in  the  apparent  decrease  in  the 
length  of  those  cirri  in  the  median  line  of  the  mouth. 

In  figs.  35,  36  and  37,  different  aspects  of  the  mouth  of  an  adult  individual  are  shown; 
figs.  35  and  36  representing  the  outline  of  the  mouth  alone,  while  in  fig.  37  the  cirri 
are  shown.  In  these  three  views  the  oral  tubercle  (ot),  as  it  may  be  called,  is  strongly 


EARLY    STAGES    OF    TEREBRATULINA.  35 

marked.  The  same  projection  is  represented  in  the  mouth  of  Thecidlum  Mediterraneum, 
as  figured  by  Lacaze-Duthiers.  A  singular  lunate  groove,  running  parallel  with  the  free 
lip,  is  indicated  in  the  figures,  which  may  be  called  the  oral  groove  (og).  It  seems  more 
like  a  wrinkle  caused  by  the  expansion  of  the  free  lip,  though  its  limits  are  well  defined 
and  the  furrow  is  quite  deep. 

The  independent  movements  of  the  cirri  are  shown  in  fig.  37  ;  these  are  just  as  pliant 
in  their  movements  as  in  those  of  the  extreme  young,  and  at  all  times  recall  the  motions 
of  the  cirri  in  the  Polyzoa. 

Structure  of  the  Shell.  In  the  younger  stages  of  the  shell  the  peculiar  scale-like  struc- 
ture may  be  studied  to  the  best  advantage.  The  scales  are  few  in  number,  but  slightly 
overlapping,  and  form  a  layer  quite  distinct  from  the  outer  layer,  which  appears  to  be 
homogeneous,  save  the  concentric  lines  of  growth  appearing  like  rows  of  oblong  and  flat- 
tened nodules.  The  terminal  portions  of  the  pallial  caeca  within  or  upon  this  outer  layer, 
are  brown  in  color  and  distinctly  granulated.  I  failed  to  make  out  anything  satisfactory 
regarding  the  character  of  these  peculiar  parts.  In  a  few  doubtful  cases  I  thought  I  saw 
one  or  two  tubules  radiating  from  the  terminal  ends  of  the  caeca,  and  in  fig.  38,  A,  one 
observation  is  represented.  It  will  be  seen  by  this  that  the  tubules  radiate  from  the 
largest  diameter  of  the  caeca,  and  not  from  the  periphery  of  the  granulated  disk,  and  this 
is  in  accordance  with  the  admirable  observations  made  by  King.1  The  scales  do  not 
appear  to  encroach  upon  the  walls  of  the  caeca. 

Fig.  38  shows  a  small  fragment  of  the  shell  at  an  early  stage  ;  portions  of  five  scales 
are  here  seen  forming  the  inner  layer  of  the  shell.  In  the  earlier  stages,  when  they  are 
large  and  few  in  number,  the  scales  are  flat ;  now  and  then  showing  a  raised  line  caused 
by  the  encroachment  of  two  superincumbent  scales,  between  which  the  under  scale  is 
closely  adjusted.  This  may  be  seen  in  fig.  39,  and  better  in  fig.  40,  where  the  ends  of 
the  scales  are  broken,  and  show  in  section  ;  also  in  fig.  41,  where,  in  a  later  stage,  they 
become  more  numerous ;  here  the  terminal  ends  of  five  scales  are  shown  in  juxtaposition. 

In  fig.  42  a  portion  of  the  anterior  margin  of  one  valve  is  shown.  The  newly  formed 
scales  are  just  indicated  near  the  border,  beyond  which  the  outer  layer  projects. 

Fig.  43  represents  two  scales  from  a  stage  still  more  advanced ;  here  the  numerous 
lines  upon  the  scales  indicate  their  closer  aggregation.  As  the  shell  increases  in  age,  the 
scales  become  more  attenuated,  and  now  the  scale  is  diverted  wherever  it  encounters  a 
csecal  process,  and  forms  a  yoke  or  loop  around  it. 

In  fig.  15,  plate  i,  a  few  spiculas  at  the  base  of  the  cirri  mark  the  commencement  of 
the  calcareous  loop.  At  a  later  stage  the  spiculae  increase  rapidly  in  number,  and  finally 
anastomose,  appearing  as  in  fig.  44.  The  scales  composing  the  base  of  the  crura  are 
acicular  in  shape,  and  run  parallel  with  the  crural  axis.  In  adult  specimens  the  scales  of 
the  crural  supports  resemble  acicular  crystals,  and  when  boiled  in  a  solution  of  caustic 
potash,  glisten  and  separate,  resembling  the  fibres  of  asbestos  (fig.  47). 

Fig.  46  represents  the  crural  process  of  one  side,  taken  from  a  specimen  less  than  an 
eighth  of  an  inch  in  length.  It  exhibits  the  first  stages  of  the  loop.  The  acicular  scales 
are  shown  at  the  base,  while  the  remaining  portion  is  made  up  of  scales  similar  to  those 

1  Prof.  W.   King,  on   the   Histology  of   the  Test  of  the      Academy,  vol.  xxiv,  pt.  xi,  1869. 
Class  Palliobranchiata.      Transactions    of   the   Koyal   Irish 


36  EARLY    STAGES    OF    TEREBRATULINA. 

composing  the  shell.  From  an  extremely  young  specimen  I  observed  these  same  peculiar 
acicular  scales  (fig.  45),  and  they  probably  indicate  the  presence  of  the  crura. 

Nothing  of  a  satisfactory  nature  was  made  out  regarding  the  structure  of  the  shell  in 
the  earliest  stage  (fig.  2,  plate  i),  though  had  the  shell  possessed  the  peculiar  scale-like 
structure  and  cascal  perforations,  they  would  have  been  visible. 

Growth  of  the  Shell.  Figs.  18,  19  and  20,  plate  I,  severally  show  portions  of  the 
haamal  valve,  neural  valve,  and  the  valves  connected,  from  an  early  lingula-form  stage. 
In  fig.  18,  the  hinge  plate  (hp)  and  the  dental  socket  (ds]  are  well  marked;  in  the  earlier 
stages  of  their  development  the  crura  appear  as  slight  projections.  In  fig.  19  the  promi- 
nence of  the  so-called  teeth  of  the  shell  (te)  is  given. 

Fig.  20  represents  the  valves  joined ;  the  caeca  are  seen  perforating  the  entire  margin 
of  the  shell  about  the  foramen,  which  is  very  wide  and  rudimentary. 

On  plate  n  a  series  of  stages  are  given  to  show  the  gradual  development  of  the  crura, 
and  parts  surrounding  the  foramen.  The  upper  line  of  figures  in  this  series,  marked  N, 
represents  the  neural  or  ventral  valve,  and  the  lower  line  of  figures,  miirked  n,  represents 
the  haemal  or  dorsal  valve.  In  the  youngest  of  these  stages,  figs.  48  and  49,  a  broad  gap 
in  the  neural  valve  indicates  the  peduncular  foramen.  It  will  be  seen  that  the  shell  is 
folded  upon  each  side  of  the  peduncular  passage.  These  folds  never  meet  in  this  species. 

Figs.  50  and  51  show  a  slightly  more  advanced  stage,  the  difference  being  mainly  in 
the  greater  prominence  of  the  crura. 

In  the  next  stage,  figs.  52  and  53,  the  calcareous  loop  is  well  advanced,  though  not  yet 
connected  by  a  continuous  shelly  layer,  though  at  all  stages  these  portions  are  connected 
by  a  membrane  charged  with  spiculae.  Figs.  54  and  55  represent  similar  portions  of  an 
adult  shell  for  comparison.  It  will  be  seen  that  the  neural  process  of  the  loop  becomes 
connected,  while  the  haemal  process  does  not  become  so  connected,  though  in  some  speci- 
mens it  closely  approximates.  The  peduncular  opening  becomes  more  circular,  and  the 
cardinal  process  (cp),  which  does  not  appear  in  the  earlier  stages,  is  now  present. 

Figs.  56,  57  and  58  are  added,  to  exhibit  the  relative  outlines  of  the  more  prominent 
stages  in  the  growth  of  the  shell.  Compare,  also,  fig.  2,  plate  i,  where  the  shell  is  as 
long  as  it  is  broad,  and  the  hinge  margin  represents  the  greatest  transverse  diameter  of 
the  animal.  In  fig.  56  the  shell  elongates,  with  the  sides  nearly  parallel,  and  the 
peduncular  opening  wide  and  gaping.  (The  line  accompanying  the  figures  represents  the 
natural  size  of  the  shell.)  Fig.  57  represents  a  stage  intermediate  between  the  lingula 
form  and  the  adult ;  the  peduncular  opening  is  more  contracted,  the  sides  of  the  shell 
are  no  longer  parallel,  though  the  hinge  margin  has  nearly  the  same  outline  as  in  the  first 
stage.  Fig.  58  represents  the  adult  shell.  Here  the  outline  assumes  entirely  different 
proportions,  being  nearly  oval,  while  the  hinge  margin  forms  a  sharp  angle,  and  the  fora- 
men is  quite  circular. 

Relations  with  the  Polyzoa.  The  general  affinities  of  the  Brachiopoda  with  the  Poly- 
zoa,  as  indicated  by  Milne  Edwards,  Huxley,  Hancock,  Agassiz,  Hyatt  and  others,  are 
admitted  by  most  zoologists. 

In  the  preceding  examinations  of  the  early  stages  of  Terebratulina,  we  have  additional 
evidence  of  their  relationship.  In  the  evolution  of  the  lophophore,  from  its  circular  char- 
acter, surmounted  by  a  few  cirri,  to  that  of  the  hippocrepian  stage,  we  have  suggested, 
first,  the  circular  lophophore  in  the  inferior,  or  Gymnolajmatous  Polyzoa,  and  finally,  the 


EARLY  STAGES   OF  TEREBRATULIXA.  37 

bilateral  lophophore  of  the  superior,  or  Phylactolrematous  Polyzoa.  The  brachial  fold,  a 
delicate  membrane  bordering  the  lophophore,  immediately  within  which  the  cirri  spring, 
as  seen  in  Lingula  and  Discina,  may  properly  be  compared  to  the  calyx  in  the  higher 
Polyzoa.  Still  later  the  presence  of  a  distinct  fold  bordering  the  mouth,  very  pliant  and 
active,  may  be  compared  as  to  function  and  position,  with  the  epistome  of  the  Polyzoa, 
though  not  occupying  an  homological  position  in  regard  to  flexure  of  intestine.  It  would 
appear  that  the  membranes  suspending  the  stomach  and  intestine  in  the  perivisceral  cavity, 
have  some  relation  to  the  funiculus  in  the  Polyzoa.  In  Paludicella  there  are  two  flexible 
cords  connecting  the  stomach  and  the  endocyst,  called  by  Allman  the  anterior  and  posterior 
funiculus,  to  which  are  attached  respectively  the  ovary  and  testis.  In  Lingula  and  Dis- 
cina we  find  the  reproductive  organs  attached  to  bands,  that  connect  the  stomach  and 
intestine  to  the  perivisceral  wall.  In  Alcyonella  the  ovary  arises  from  the  endocyst,  and 
likewise  in  Terebratulina  and  allied  genera  we  find  the  mantle,  or  endocyst,  holding  the 
reproductive  organs. 

The  early  appearance  of  the  divaricator  muscles  in  Terebratulina  would  justify  Mr. 
Hyatt  in  his  views,  that  these  muscles  represent  the  retractors  of  the  Polyzoa.1 

The  combination  of  the  stomach  and  intestine  in  their  early  stages,  with  the  presence 
of  hepatic  cells  lining  their  inner  walls,  and  the  presence  also  of  a  cardiac  valve  or  con- 
striction, all  recall  similar  parts  in  the  higher  Polyzoa. 

That  these  relations  may  be  carried  farther,  there  is  no  reason  to  doubt.  Fritz  Miiller 
has  noted  in  an  early  stage  of  some  species  of  Discina  (though  from  observations  I  have 
made  in  Lingula  pyramidata,  the  embryoes  examined  by  him  are  as  likely  to  belong  to 
this  genus,  as  to  Discina)  several  sets  of  seta),  which  project  from  the  body  and  are  capa- 
ble of  locomotion.  F.  A.  Smitt 2  has  noticed  in  the  development  of  Lepralia  Peachii,  a 
cluster  of  six  bristles  bent  at  their  points,  that  from  time  to  time  were  drawn  in  and  again 
thrust  out. 

With  propriety  may  also  be  suggested  a  certain  parallelism  between  the  leading  groups 
of  the  Polyzoa  and  the  Brachiopods.  We  have  fonns,  like  Lepralia,  attached  by  one 
region  of  their  shell,  this  shell  being  calcareous  and  exhibiting  minute  punctures,  which 
have  been  compared  to  similar  markings  in  certain  Brachiopods.  So  among  the  latter 
group  do  we  find  forms  attached,  as  in  Thecidium,  and  some  species  of  Productus ;  and 
generally  the  articulate  Brachiopods  might  be  compared  to  such  forms  as  Lepralia,  while 
on  the  other  hand  such  genera  as  Pedicellina,  with  its  long,  pliant  and  muscular  stalk,  or 
Loxosoma,  with  a  stalk  highly  retractile,  may  be  compared  to  Lingula.  The  limits  or 
intentions  of  this  paper  will  not  allow  any  considerations  regarding  the  relations  of  the 
Brachiopods  with  the  other  groups  of  the  animal  kingdom.  I  have  elsewhere 3  expressed 
my  belief  that  they  are  true  articulates,  having  nearer  affinities  with  the  Vermes ;  and  in 
view  of  the  above  relations  of  the  Brachiopods  with  the  Polyzoa,  it  is  interesting  to  remark 

A.  Hyatt.     Observations  on  Polyzoa,  suborder  Phylacto-  8  The   Brachiopoda,   a    revision   of    Annelida,   American 

laemata.  Proceedings  Essex  Institute,  vols.  IV,  v.  Salem,  Journal  Sc-ience,  July,  1870.  Reprinted  in  Annals  and  Mag- 
Mass,  azine  of  Natural  History,  London,  no.  33,  vol.  VI,  4th  series. 

8  Om  Hafs-Bryozoernas  utveckling  och  fettkroppar.  Of- 
versigt  af  Kongl.  Vetenskaps-Akademiens  Forhandlingar. 
Stockholm,  1865. 

MEMOIRS    HOST.  SOC.   KAT.   H18T.      VOL.   II.  10 


38  EARLY  STAGES  OF    TEREBRATULINA. 

that  Leuckart  has  for  a  long  time  placed  the  Polyzoa  with  the  Vermes,  and  in  a  new 
edition  of  the  "  Outlines  of  Comparative  Anatomy,"  *  Prof.  Carl  Gegenbaur  removes  the 
Polyzoa  from  the  Mollusca,  and  associates  them  with  the  Vermes. 


EXPLANATION   OF   PLATES. 

PLATE     I. 

Fig.  1.     A  few  eggs  in  their  natural  position,  from  pallial  membrane  of  an  adult  individual. 

Fig.  2.     Earliest  stage  noticed.     This  was  attached   to  rock,  resting  upon  broad   hinge  margin. 

Fig.  3.  Another  stage  in  which  the  body  has  rapidly  lengthened,  and  the  peduncle  is  equal  in  length  to 
the  remaining  portion  of  the  animal. 

Fig.  4.     Stage  in  which  a  few  cirri  are  developed  with  the  oesophagus  and  stomach  hanging  below. 

Figs.  5,  6,  7.  CEsophagus  and  stomach  of  last  individual,  showing  different  conditions  of  expansion  and 
contraction  of  the  parts. 

Figs.  8,  9.    Partial  lateral  views  of  the  shell  of  fig.  3. 

Fig.  10.     Represents  the  animal  at  rest,  and  in  action. 

Fig.  11.     The  same  from  above;  the  arrows  indicating  the  direction  of  rotation. 

Fig.  12.    A  state  more  advanced,  with  the  liver  as  a  simple  hepatic  fold  on  each  side  of  the  stomach. 

Figs.  13,  14.  Different  states  of  contraction  of  incipient  hepatic  folds  of  fig.  12 ;  and  showing  cardiac 
contraction  in  fig.  14,  c. 

Fig.  15.  Crown  of  cirri  to  show  calcareous  spiculse.  [For  distinctness  and  to  simplify  the  drawings,  the 
cilia  clothing  the  cirri  are  only  shown  in  fig.  4,  the  simple  outline  of  cirri  in  fig.  ]2  and  the  calcareous  spiculae 
in  fig.  15.  It  will  be  understood,  however,  that  each  figure  possesses  all  the  characters  of  the  others.] 

Fig.  16.     Portions  of  two  cirri  highly  magnified  to  show  more  plainly  the  form  of  spiculas. 

Fig.  17.  Alcoholic  specimen  in  which  divaricator  muscles  were  visible  owing  to  contraction  of  the  parts 
in  alcohol.  This  is  the  only  figure  drawn  from  a  preserved  specimen.  All  the  others  are  from  life. 

Fig.  18.    A  portion  of  haemal  valve. 

Fig.  19.    A  portion  of  neural  valve. 

Fig.  20.    The  same  portions  before  separation. 

Fig.  21.     A  slightly  more  advanced  stage,  showing  crown  of  cirri. 

Fig.  22.  A  still  more  advanced  stage,  with  haemal  valve  forcibly  thrown  open,  showing  divaricator  muscles 
with  stomach  between.  The  crown  of  cirri  shows  first  indications  of  its  bilobud  character. 

Fig.  23.     An  hepatic  mass  from  one  side ;  at  this  stage  showing  the  first  forming  of  caecal  folds. 

Fig.  24.     A  stage  more  advanced ;  valves  forcibly  separated  in  which  all  the  parts  are  plainly  seen. 

Fig.  24,  A.  A  highly  magnified  view  of  the  stomach,  hepatic  folds,  lateral  bands,  etc.,  of  fig.  24.  This 
figure  shows  a  faecal  mass  rolled  in  a  spiral  form,  in  the  act  of  being  discharged  through  the  mouth.  The  line 
bordering  the  upper  portion  of  the  figure  indicates  the  inferior  margin  of  the  crural  process. 

Fig.  25.     The  haemal  valve  with  crown  of  cirri,  etc. 

Fig.  26.    A  view  of  fig.  22  with  the  valves  closed. 

PLATE    II. 

Fig.  27.  A  stage  considerably  more  advanced  than  preceding  ones,  showing  lophophore  already  bilobed, 
the  cirri,  however,  not  deflected.  The  caecal  lobules  of  liver  few  in  number  but  separated.  In  fig.  23,  plate  I, 
the  lobules  are  just  indicated. 

Fig.  28.     Showing  lophophore,  with  cirri  deflected.     The  stomach  and  blind  intestine  hanging  below. 

Fig.  29.  The  arms  of  the  lophophore  more  sharply  bent;  the  central  processes  first  indicated.  The  highly 
flexible  lip  is  here  seen  in  folds. 

1  Grumkiige  der  Vergleichenden  Anatomie.     Zweite  ungcarbeitete  Auflage.     Leipzig,  1870. 


EARLY  STAGES  OF  TEREBRATULINA. 


39 


Fig.  30.  A  stags  slightly  more  advanced  than  the  preceding.  The  lip  is  seen  thrown  back,  disclosing  the 
capacious  mouth. 

Fig.  31.     Another  view  of  the  same  opening. 

Fig.  32.  A  stage  more  advanced,  in  which  the  lophophore  begins  to  assume  the  characters  of  the  adult. 
The  cirri  are  now  more  numerous  and  more  attenuated,  and  the  lip  is  not  so  widely  reflected. 

Figs.  33,  34.     Showing  the  mouth  of  fig.  32  in  different  states  of  contraction. 

Figs.  35,  36,  37.     Views  of  the  mouth  of  an  adult  individual,  showing  oral  tubercle,  and  oral  groove. 

Fig.  38.  Fragment  of  shell  highly  magnified,  showing  scales,  tubules  and  outer  layer,  with  lines  of  accre- 
tion indicated  by  rows  of  flattened,  bead-like  nodules. 

Fig.  38,  A.     Exterior  portion  of  tubule,  showing  radiating  pores. 

Fig.  39.     Single  scale. 

Fig.  40.     Single  scale,  broken  across,  and  showing  ridge  in  section. 

Fig.  41.     Five  scales  in  position. 

Fig.  42.     Fragment  of  anterior  portion  of  haemal  valve. 

Fig.  43.     Two  scales  from  an  adult  specimen. 

Fig.  44.     Portion  of  crural  process  from  early  stage. 

Fig.  45.     Acicular  scales  from  early  stage. 

Fig.  46.     Right  crural  process,  from  early  stage. 

Fig.  47.     Acicular  scales  from  base  of  crural  process  of  adult. 

Figs.  48,  49,  50,  51,  52,  53.  Portions  of  haemal  and  neural  valves  of  early  stages  showing  development  of 
crura. 

Figs.  54,  55.     Corresponding  parts  of  adult,  natural  size. 

Figs.  56,  57,  58.  Outlines  representing  different  stages  from  extreme  young  to  adult,  fig.  58  being  natural 
size. 

NOTE. — No  means  of  measurement  were  at  hand  when  the  original  studies  were  made.  A  Hue  enclosed  by 
a  circle  indicates  the  entire  length  of  the  shell  from  which  the  parts  were  drawn.  Where  the  size  is  not 
indicated,  it  will  be  understood  that  the  parts  are  from  equally  young  stages,  unless  otherwise  described  in 
the  explanation  of  plates. 

EXPLANATION   OF   LETTERS   ACCOMPANYING  THE  FIGURES. 


m,  mouth. 

e,  epistome. 
ce,  oesophagus. 
a,  stomach. 

c,  cardia. 

t,  intestine. 

f,  faeces. 

vm,  ventral  mesentery. 

I,  liver. 

h,  hepatic  cells. 

Off,  oral  groove. 

ot,  oral  tubercle. 

d,  divaricator  muscles. 

Ib,  lateral  gastro-parietal  bands. 

p,  peduncle. 

pa,  point  of  attachment  of  peduncle. 

se,  setae. 

cm,  pallial  caecum. 


t,  cirn. 

g,  granules  passing  to  and  fro  from  liver  to  intes- 
tine. 

cr,  crura. 

cl,  calcareous  loop. 

ex,  external  shell  layer,  of  a  chitinous  nature. 

in,  internal  shell  layer,  of  calcareous  scales. 

cce,  pallial  caeca. 

hp,  hinge  plate. 

cp,  cardinal  process. 

ds,  dental  sockets. 

fo,  foramen. 

te,  teeth  of  shell. 

cs,  calcareous  spiculae. 

en,  notch  for  pallial  caeca. 

H,  haemal  valve. 

N,  neural  valve. 


uirs  Boston  Soc.Nat.Hist.Vol.il. 


PL  I. 


WU-CHORLTON  J»  3P 


EDW.  S.MORSE. ON  THE. EARLY  STAGES  OFTEREBRATULI  NA  . 


Memoirs  Boston  Soc.  Nat.  Hist  .Vol.  II. 


PHI 


gv        <3><&vPci'  <;  si-, 

7*.  £< 

'•j\          T^M  5  ' 


EDW.S  MORSE  ON  THE  EARLY  STAGES  OF TEREBRATULINA. 


EMBRYOLOGY  OF  TEREBRATULINA. 


BY  EDWARD  S.  MORSE,  PH.D., 

PROFESSOR  OF  COMPARATIVE  ANATOMY  AND  ZOOLOGY  IN  BOWDOIN  COLLEGE. 


From  the  Memoirs  of  the  Boston  Society  of  Natural  History,  Vol.  II. 


EMBRYOLOGY  OF  TEREBRATULINA. 


BY  EDWARD  S.  MORSE,  PH.D., 

PKOFESSOB  OF  COMPARATIVE  ANATOMY  AND  ZOOLOGY  IN  BOWDOIN  COLLEGE. 


, 


VIII.    EMBRYOLOGY  OF  TEREBRATULINA.    BY  EDWARD  S.  MORSE. 

YV ITH  the  great  impulse  given  to  the  study  of  Zoology  through  the  labors  of  Charles 
Darwin,  renewed  effort  has  been  made  to  work  up  the  embryology  of  those  forms  which 
have  rendered  so  little  satisfaction  from  the  study  of  their  mature  characters,  and  thus 
through  the  labors  of  European  naturalists  new  light  has  been  thrown  upon  the  develop- 
mental history  of  Sagitta,  Amphioxus,  the  Tunicates,  and  many  other  aberrant  groups. 
And  now  while  the  embryology  of  nearly  every  prominent  group  has  been  more  or  less 
studied,  and  important  relations  revealed  that  would  have  otherwise  been  obscured,  little 
or  nothing  has  been  done  to  throw  any  light  on  the  embryology  of  the  Brachiopods,  a 
class  represented  by  thousands  of  species  in  past  times,  and  one  of  which  we  have  the 
earliest  records  in  the  rocks. 

This  dark  portion  in  the  history  of  the  Brachiopods  seems  all  the  more  strange  when  we 
recall  the  many  beautiful  monographs  of  various  genera  of  Brachiopods  published  since 
Cuvier's  famous  memoir,  in  the  year  1802,  on  Lingula,  and  when  it  is  remembered  that  a 
hundred  and  more  species  still  exist  in  the  seas  at  present.  What  little  has  been  accom- 
plished in  this  field,  however,  has  shed  great  light  on  the  natural  affinities  of  the  class,  and 
it  may  be  well  briefly  to  recall  what  has  already  been  done  in  order  to  make  this  portion  of 
their  history  more  complete. 

To  Oscar  Schmidt  is  due  the  credit  of  giving  the  first  figure  of  a  larval  Brachiopod.  In 
the  "  Zeitschrift  fiir  ges.  Naturwissenschaften,"  1854,  p.  325,  he  gives  a  description  of 
the  embryo  of  some  species  of  Terebratula  collected  in  the  North  Sea.  Accompanying 
this  description  a  simple  figure  was  given.  In  this  the  embryo  shows  a  deep  constric- 
tion in  the  centre,  the  free  or  cephalic  portion  being  wider  than  the  posterior  half,  which 
is  abruptly  truncate  at  the  end,  and  he  infers,  and  rightly  too,  that  at  this  end  the  embryo 
becomes  attached.  I  add  a  brief  translation  of  his  description. 

The  embryos  of  the  Norwegian  Terebratula  observed  by  me  differ  remarkably  from  the  embryo  Lingula 
as  described  by  Owen.  They  resemble  a  Euastrum  composed  of  unequal  halves;  the  round  end  seems  to  be 
the  anterior.  The  somewhat  narrower  hinder  portion  extends  into  two  projections.  In  none  of  the  ovaries 
examined  by  me  —  for  in  these  were  the  embryos  found  —  had  the  development  gone  farther.  In  the  per- 
fect ignorance  in  which  we  now  are  with  regard  to  the  development  of  Terebratula,  every  small  contribution 
towards  clearing  up  this  question  is  acceptable.1 

1  The  allusion  to  the  embryo  Lingula  of  Owen  has  refer-  ova.     In  one  egg  he  suggests  the  rudiments  of  a  peduncle, 

ence  to  Prof.  Owen's  memoir  on  the  Anatomy  of  Terebratu-  The  egg,  as  it  escapes  from  the  ovary  by  dehiscence,  often 

Una,  forming  the  introduction  to  Davidson's  British  Fossil  presents  the  appearance  figured  by  him,  from  the  thin  mem- 

Brachiopoda,  published  by  the  Palieontolographical  Society,  brane  still  adhering  to  the  egg  after  its  rupture,  and  conse- 

London.     On  Plate  i.  of  the  Introduction,  Owen  figures  five  quent  separation,  from  the  cluster. 
eggs  of  Linyiila  anatitia,  which  he  supposes  are  impregnated 


MEMOIRS    BO6T.    SOC.    NAT.    HIST.     VOL.    II. 


250  EMBRYOLOGY  OF  TEREBRATULINA. 

To  Lacaze-Duthiers,  however,  is  due  the  credit  of  first  presenting  several  stages  in  the 
embryology  of  a  Brachiopod.  In  a  memoir :  upon  the  curious  form  Thecidium,  from  the 
Mediterranean,  he  figures  the  egg,  as  well  as  several  subsequent  stages  in  the  early  history 
of  the  embryo.  These  were  found  in  a  pouch  attached  to  the  cirri  and  contained  within 
the  pallial  cavity.  The  embryo  is  first  divided  into  two  transverse  segments,  then  into 
three,  and  finally  into  four  segments.  In  one  embryo  he  found  two  red  ocular  points 
upon  the  cephalic  ring,  in  another  four  red  eye  spots  occurred. 

In  one  figure  he  represents  the  rings  contracted  upon  each  other,  as  will  be  seen  to  be 
the  case  with  the  embryo  of  Terebratulina.  As  before,  I  shall  give  the  reader  a  condensed 
translation  of  the  paper. 

The  youngest  egg  studied  had  already  a  somewhat  pyriform  and  elongated  shape.  The  most  striking  fact 
was  the  size  of  the  cells  composing  it,  and  which  themselves  enclosed  a  great  quantity  of  granules  of  rela- 
tively very  large  size.  The  cells  no  doubt  were  the  result  of  segmentation,  and  the  granules  must  have 
appeared  during  the  first  movements  of  embryonic  activity,  for  the  vitellus  had  only  very  minute  granules. 

In  the  next  stage  frequently  seen  after  the  preceding,  and  which  I  have  observed  in  the  same  lot  of  young, 
the  embryo  divided  into  two  lobes,  the  larger  being  always  attached  to  the  suspensory  filament.  In  the 
embryo  so  divided  by  a  circular  furrow,  perpendicular  to  the  longer  axis,  the  mass  has  a  yellow  tint,  and  is 
no  longer  composed  of  large  cells,  but  is  filled  with  yellow  granulations  much  finer,  and  enclosed  in  smaller 
cells.  In  the  smaller  lobe  a  clearer  space  is  seen,  where  the  cells  are  filled  with  nearly  colorless  granules.  On 
each  side  of  the  larger  lobe  also,  and  very  near  the  transverse  furrow,  are  two  transparent  spaces  smaller  than 
the  preceding,  but  similar  in  other  respects. 

The  larger  lobe,  attached,  as  stated,  to  the  suspensory  filament,  is  the  anterior ;  the  faces  cannot  yet  be  dis- 
tinguished ;  but  later  it  is  possible  to  recognize  the  superior  or  inferior  aspect. 

The  development,  therefore,  commences  by  the  appearance  of  the  two  lobes,  one  the  anterior,  with  two 
white  spots,  and  the  other  with  a  single  clear  spot ;  later  other  spots  with  less  coloring  matter  appear.  Thus 
there  appears  near  the  point  of  attachment,  on  each  side  of  the  peduncle,  a  clear  white  spot,  then  the  two 
lateral,  spots  above  referred  to,  grow  longer  and  obliquely  extend  towards  the  centre  of  the  lobe. 

Between  these  two  last  spots,  on  the  line  of  separation  between  the  lobes,  the  colored  granules  accumulate 
and  form  these  lobules,  the  median  later  extending  toward  the  posterior  lobe. 

The  posterior  lobe  itself  does  not  increase  in  proportion  to  the  rest  of  the  embryonic  mass,  but  the  trans- 
parent spot  begins  to  show  what  it  will  later  become.  It  extends  towards  the  place  where  the  lobules  com- 
mence, then  it  becomes  depressed  in  the  middle,  and  will  form,  in  fact,  a  real  depression.  There  is  still  a  gap 
between  this  and  the  succeeding  stage  to  be  described.  The  two  white  lateral  bands,  near  the  separation  of 
the  lobes,  are  traces  of  the  formation  of  a  new  lobe,  for  the  anterior  lobe  divides  into  two  by  a  transverse 
furrow,  and  these  two  anterior  lobes  always  remain  relatively  very  large,  the  posterior  changing  but  little. 

At  the  time  when  this  division  takes  place,  toward  the  point  of  attachment  where  two  other  little  clear 
spots  have  been  seen,  a  lobule  rises,  which  forms  the  counterpart  of  the  little  primitive  posterior  lobe.  Thus 
the  embryo  is  composed  of  four  portions,  two  large  in  the  middle  and  two  smaller  at  the  ends. 

If  the  embryo  is  examined  on  all  sides,  it  is  soon  seen  that  the  two  poles  of  the  ovoid  embryo  are  bent 
towards  each  other  on  one  side,  as  if  the  two  anterior  lobes  were  curved  over  towards  the  two  posterior. 
The  concave  face  may  be  considered  as  the  inferior,  and  the  convex,  the  dorsal  aspect. 

The  insertion  of  the  suspensoiy  peduncle  is  on  the  dorsal  side  of  the  anterior  extremity,  on  the  back  of  the 
little  anterior  lobule,  not  far  from  the  edge  of  the  second  lobe.  This  peduncle  is  cellular,  and  composed  of 
very  distinct  elements,  and  easy  to  recognize.  The  embryo  is,  therefore,  suspended  by  the  back  of  the  head. 

The  inferior  side  of  the  anterior  lobule  is  fiat  and  somewhat  quadrilateral  in  the  most  developed  embryo  seen ; 
near  the  middle  is  a  sort  of  oval  longitudinal  slit,  which  appears  to  be  the  mouth,  although  I  have  never  seen 
particles  of  coloring  matter,  which  I  have  put  into  the  surrounding  liquid,  penetrate  this  opening,  but  indeed 
the  embryos  are  still  too  young  to  feed. 

1  Annales  des  Sci.  Nat.,  4*  Serie,  Vol.  XV.,  p.  317. 


EMBRYOLOGY  OF  TEREBRATULIXA.  251 

On  the  inferior  side  also  of  the  lobule,  somewhat  deeply  seated  in  the  tissues,  appear  some  red  dots  sym- 
metrically placed  on  each  side.  These  spots  I  believe  to  be  eye  spots  ;  they  are  sometimes  four  in  number,  and 
sometimes  only  two.  The  presence  of  these  spots  and  of  the  slit,  lead  me  to  consider  this  extremity  as 
anterior. 

The  second,  or  large,  anterior  lobe  is  swollen  behind,  and  nearly  flat  beneath.  Its  posterior  edges  run  ob- 
liquely backward  to  form  a  very  obtuse  angle,  hardly  closed  on  the  ventral  side  of  the  large  posterior  lobe, 
extending  towards  the  angle  made  by  the  posterior  lobule,  which  seems  to  be  hollowed  out  with  a  wide 
depression. 

The  embryos,  when  the  peduncle  is  broken,  swim  and  whirl  round  by  means  of  the  cilia  clothing  the  lobes. 
The  anterior  extremity  moves  forward  always.  The  embryos  are  very  contractile,  so  that,  often  on  meeting 
an  obstacle  the  longitudinal  diameter  becomes  shorter  than  the  transverse,  the  two  extremities  contracting 
towards  each  other.  The  cilia  then  stop  and  seem  to  disappear. 

It  has  not  been  possible  to  carry  the  observations  farther. 

To  sum  up,  then,  on  the  inferior  aspect  one  of  the  most  advanced  embryos  shows  four  eye  dots,  as  well  as 
a  distribution  of  the  yellow  material  in  the  midst  of  the  large  anterior  lobe,  which  reminds  one  much  of  the 
origin  of  the  liver  in  the  Acephala  or  Gasteropoda,  and  it  is  probable  that  the  alimentary  tract  is  hollowed  out 
in  the  middle  of  these  yellow  granules,  so  that  the  secretory  lobules  of  the  liver  of  the  adult  Thecidium  are 
foreshadowed  in  these  series  of  little  packets. 

In  the  early  summer  of  1872  I  was  fortunate  in  tracing  the  embryology  of  Terebratu- 
lina  so  far  as  to  carry  the  embryo  to  a  form  with  three  well  marked  and  deeply  constricted 
segments,  and  saw  enough  at  that  time  to  convince  me  that  the  embryo  became  attached  by 
its  caudal  segment.  These  meagre  results  were  published  in  Silliman's  Journal.1 

Some  interesting  features,  however,  had  been  brought  to  light  in  studying  the  early 
stages  of  certain  Brachiopoda,  the  most  important  of  which  were  presented  by  Fritz 
Miiller  in  a  note  published  in  Reichert  und  Du  Bois-Reymond's  Archiv,  1860,  p.  72,  and 
a  subsequent  note  in  Wiegmann's  Archiv,  1861,  p.  53.  These  notes  referred  to  the  early 
stages  of  a  form  supposed  to  be  Discina,  collected  at  Santa  Catharina,  Brazil.  I  subjoin 
the  notices  which  were  published  in  the  Annals  and  Magazine  of  Natural  History,  3d  series, 
Vol.  vi.,  p.  310. 

''  Dr.  F.  Mtiller  has  sent  from  Brazil  the  description  of  a  larva  belonging  undoubtedly  to  a  Brnchiopod, 
which  is  the  more  interesting,  as  the  Brachiopoda  are  the  only  Mollusca  regarding  the  development  of  which 
we  have  no  information. 

"The  larva  in  question  is  a  small,  perfectly  orbicular,  bivalve  Mollusk.  The  two  valves  are  similar,  but  un- 
equal in  size,  the  dorsal  valve  being  the  largest.  At  the  place  of  the  hinge  a  small  oval  plate  is  placed  trans- 
versely between  the  two  valves  of  the  shell.  The  mantle  is  gaping  all  round.  Five  pairs  of  very  stiff  setae, 
of  which  one  is  much  stronger  than  the  others,  and  curved  backwards,  project  at  the  periphery.  They  origi- 
nate in  the  mantle  of  the  ventral  half;  at  least  this  is  the  case  with  four  of  them.  A  series  of  finer  setse 
spring  from  the  circumference  of  the  mantle  of  the  dorsal  valve,  and  curve  down  upon  the  outside  of  the 
ventral  valve.  The  animal,  as  well  as  the  shell,  would  be  divided  into  two  symmetrical  halves  by  a  plane 
drawn  vertically  through  the  middle  of  the  hinge.  The  body,  which  is  furnished  with  an  alimentary  canal, 
two  auditory  capsules,  and  two  eyes,  fills  the  posterior  half  of  the  space  between  the  valves.  The  anterior 
half  is  occupied  by  four  pair  of  cylindrical  arms,  between  which  a  rounded  knob  is  situated.  Behind  the 
knob  the  mouth  is  perceptible. 

"  These  four  pair  of  arms  are  supported  upon  a  common  peduncle,  at  the  extremity  of  which,  therefore,  the 
mouth  is  placed.  The  arms  are  covered  with  a  very  well  developed  ciliary  coat,  by  the  agency  of  which  the 
little  animal  swims.  The  reproductive  and  circulatory  organs  are  wanting. 

"During  natation  the  mouth  is  always  directed  forwards,  which  is  in  favor  of  the  generally  received  opinion 

1  Am.  Jour.  Science  and  Arts,  iv.,  1872,  2C2, 


252  EMBRYOLOGY  OF  TEREBRATULINA. 

as  to  the  anterior  and  posterior  regions  in  the  Brachiopoda.  It  is,  in  fact,  now  evident  that  the  Brachiopods 
are  depressed  animals,  having  an  anterior  or  ventral,  and  a  posterior  or  dorsal  valve.  MM.  Agassiz  and 
Vogt  are  therefore  wrong  in  regarding  them  as  compressed  animals  like  the  Lainellibranchiate  Mollusks ;  that 
is  to  say,  as  animals  having  a  right  and  left  valve. 

"  The  larva,  moreover,  can  not  only  swim,  but  also  creep.  This  latter  mode  of  progression  is  effected  by  a 
sort  of  rotation  of  the  ventral  valve  alternating  to  the  right  and  left.  In  this  movement  the  animal  pushes 
by  supporting  itself  principally  upon  the  strongest  of  the  bristles  above  mentioned." 

In  Wiegmann's  Archiv,  Dr.  Miiller  communicates  additional  observations  on  the  larval 
Discina,  a  notice  of  which,  follows  from  the  Annals  and  Magazine  of  Natural  History, 
3d  Series,  Vol.  vin.,  p.  505. 

"  In  the  Annals  for  October,  1860,  p.  310,  we  gave  a  short  abstract  of  a  description  of  the  larva  of  a  Brachio- 
pod  observed  by  Dr.  F.  Miiller  at  Santa  Catharina,  on  the  coast  of  Brazil ;  he  now  adds  some  further  details 
from  repeated  observations  in  the  summers  of  1859  and  1860.  The  larva  appears  to  occur  late  in  the  sum- 
mer, from  February  to  April. 

"  When  the  little  animals  are  placed  in  good-sized  vessels  with  pure  sea-water,  they  soon  ascend  slowly ;  the 
slightly  gaping  shells  stand  perpendicularly,  the  hinge-margin  downward ;  close  to  the  anterior  margin  the 
eight  arms  spread  out  horizontally  like  rays,  with  their  tips  slightly  bent  downwards  ;  and  the  roundish  knob 
situated  between  the  uppermost  pair  projects  beyond  the  plane  of  the  arms.  In  this  posture  they  move 
slowly  about  near  the  surface.  When  strongly  shaken,  or  sometimes  without  any  perceptible  reason,  they 
retract  the  arms  and  close  the  shells,  which  then  slowly  turn  over  and  sink  to  the  bottom  with  the  free  mar- 
gin downwards.  If  the  arms  be  again  protruded,  the  hinge-margin  also  again  turns  downwards. 

"  The  duration  of  this  state  never  exceeded  five  to  six  days,  and  in  general  the  larvae  adhered  to  the  bottom 
or  sides  of  the  vessel  in  a  still  shorter  time.  When  they  adhered  to  the  sides,  the  mouth  was  always  directed 
downwards ;  the  ventral  shell  was  strongly  drawn  forward  until  its  anterior  margin  reached  or  passed  that  of 
the  dorsal  shell ;  the  transversely  oval  plate,  previously  concealed  within  the  shells  (the  peduncle),  was  pro- 
truded, apparently  twisting  around  the  notched  hinder  margin  of  the  ventral  shell,  so  that  its  anterior  margin 
became  posterior.  For  a  day  or  more  the  animal  remains  contracted  and  quiet;  then,  the  shells  being 
slightly  opened,  the  arms  are  half  extended,  and  strike  inwards,  one  or  more  at  a  time,  just  as  in  the  marine 
Bryozoa.  In  a  few  days  new  bristles  appear  at  the  anterior  margin,  in  the  space  left  between  the  more  deli- 
cate setae  of  the  dorsal  shell.  In  a  week  the  author  counted  twenty  of  these,  mostly  belonging  to  the  dorsal 
shell.  The  longest  were  0.8  mill,  in  length,  straight,  colorless,  0.006  mill,  in  thickness  at  the  base,  terminat- 
ing in  a  fine  point,  unjointed  and  distantly  feathered  with  fine  lateral  setae  0.02  mill,  in  length.  The  principal 
change  in  the  soft  parts  consisted  in  the  retrogression  of  the  organs  of  sense.  The  eyes  had  become  broken  up 
into  groups  of  about  ten  black  points ;  the  previously  spherical  auditory  vescicles  were  shrunken  into  longish 
Bfics,  closely  surrounding  the  otoliths.  In  somewhat  older  animals  there  was  no  trace  of  the  organs  of  sense, 
although  they  had  not  lost  their  sensibility  to  light. 

"  One  of  the  larvae  lived  for  a  month  after  its  adhesion  ;  but  from  the  lapse  of  a  day  before  its  death  was 
noticed,  the  soft  parts  had  become  greatly  decomposed.  The  older  bristles  of  the  free  larvae  appeared  to  be 
still  present,  as  also  the  plumose  bristles  of  the  anterior  margin.  Besides  these,  there  were  on  each  side,  about 
in  the  middle  between  the  median  line  and  the  origin  of  the  great  bristles  of  the  fourth  pair,  straight,  smooth 
bristles,  0.2  mill,  in  length,  projecting  obliquely  backward,  little  thicker  than  the  strong  posterior  setae,  but 
with  a  much  stronger  outline. 

"It  is  remarkable  that  in  two  years  the  author  has  repeatedly  captured  free-swimming  larvae  which  had 
evidently  advanced  further  in  their  development  than  the  oldest  of  those  which  had  already  fixed  themselves. 
They  were  all  destitute  of  the  transversely  oval  plate,  and  of  every  trace  of  organs  of  sense;  the  plumose 
setae  of  the  anterior  margin  were  also  wanting,  as  were,  more  or  less  entirely,  the  older  bristles.  Of  the 
more  delicate  bent  bristles,  some  were  usually  still  present,  and  these  appeared  to  be  unabbreviated,  so  that 
the  missing  ones  had  probably  been  lost  by  shedding.  The  stronger  bristles,  on  the  contrary,  are  gradually 
absorbed  at  the  base ;  at  lenst  this  is  the  case  with  the  fourth  pair ;  these  were  repeatedly  met  with  of  about 
half  their  proper  length ;  the  stalk,  with  its  fusiform  dilatations,  had  disappeared,  while  the  apex  remained 
readily  recogu'z.'.ble  by  its  peculiar  curvature  and  denticulation.  In  a  still  older  animal  about  a  fifth  of  the 
length  was  still  present,  so  that  it  no  longer  extended  beyond  the  margin  of  the  shell.  This  animal  (the 
oldest  ex  iiuined  by  the  author)  had  lost  all  the  older  setse,  except  the  small  residue.  On  the  other  hand,  the 
two  straight,  smooth  bristles,  which  in  the  oldest  attached  animals  scarcely  began  to  protrude  from  the  shell, 


EMBRYOLOGY  OF  TEREBRATULINA.  253 

had  attained  a  length  of  double  the  diameter  of  the  shell,  and  being  inserted  into  thick  muscular  sheaths 
were  strongly  and  rapidly  moved  by  the  animal,  sometimes  spread  out  horizontally,  sometimes  again  crossed 
backwards. 

''•  During  this  complete  change  of 'the  setae  the  soft  parts  had  undergone  no  essential  alterations.  The 
roundish  stomach,  reaching  from  the  front  to  the  middle  of  the  longitudinal  diameter,  still  showed  the  two 
dai-k  spots  of  the  young  larvoe,  which  remind  one  of  the  similar  spots  in  the  larvae  of  some  Bryozoa,  From 
the  back  of  the  stomach  sprang  the  intestine,  which  bends  under  the  margin  of  the  stomach  to  the  right,  and 
then  forwards,  terminating  about  the  middle  of  its  right  side.  The  oesophagus  goes  from  the  front  of  the 
stomach  straight  forward  half  way  to  the  front  of  the  shell,  and  then  bends  downward,  so  that  the  mouth  lies 
close  to  the  stomach.  The  arms,  especially  the  two  middle  pair,  had  become  longer  and  slenderer,  and  the 
knob  between  the  anterior  pair  had  diminished  in  size.  No  vessels  or  pulsating  heart  were  recognized.  — 
Wiegmann's  Archiv,  p.  53,  1861.  " 

In  the  year  1869  I  communicated  to  the  American  Association  for  the  Advancement  of 
Science  the  results  of  a  study  of  the  early  stages  of  Terebratulina  sepientrionalis,  made  at 
Eastport,  Me.,  in  the  early  part  of  that  year.  This  was  afterward  published  in  the  Memoirs 
of  the  Boston  Society  of  Natural  History,  accompanied  by  two  plates. 

In  this  memoir  I  showed  the  incipient  cirri,  seven  or  eight  in  number,  and  the  gradual 
development  of  the  complicated  arms,  the  unfolding  of  the  hepatic  coeca  from  two  folds 
upon  the  walls  of  the  digestive  cavity,  the  character  of  the  shell  structure,  etc.  And  these 
two  papers  comprised  all  that  has  yet  been  done  as 'to  the  early  stages  of  the  class. 

A  wide  gap,  however,  has  existed  between  the  free  swimming  Annelidan  larva  clothed 
with  cilia  and  the  attached  form  revealing  its  Brachiopodan  character  in  the  presence  of  a 
dorsal  and  ventral  plate,  and  the  presence  of  cirri.  After  repeated  visits  to  Eastport,  al- 
most solely  for  this  purpose,  I  have  at  last  succeeded  in  closing  this  gap,  and  in  this  paper  I 
hope  to  make  plain  the  history  of  the  development  of  the  dorsal  and  ventral  areas,  the 
peduncular  attachment,  and  the  relations  the  different  parts  of  the  mature  animal  bear  to 
the  embryonic  segments,  as  well  as  to  present  some  new  features  in  the  early  stages  of 
the  species. 

For  two  seasons  I  have  found  Terebratulina  spawning  at  Eastport  during  the  last  of  May 
and  the  early  part  of  June.  It  is  probable  that  they  spawn  through  the  season,  since  I 
have  found  them  depositing  eggs  in  April.  At  my  request  Mr.  Rathbun  made  several 
observations  during  the  summer,  to  ascertain  how  long  the  species  continues  to  ovulate,  and 
he  informs  me  that  on  the  only  dates  he  collected  them,  namely,  June  26,  July  12  and 
Aug.  29,  they  were  freely  discharging  their  eggs.  It  is  best,  however,  to  study  them  as 
early  in  the  season  as  possible,  as  the  water  in  which  the  eggs  develope  must  be  kept  at  a 
low  temperature,  and  this  essential  condition  can  be  most  easily  accomplished  at  Eastport 
in  May,  where  the  temperature  at  that  time  ranges  from  forty  to  sixty  degrees  Fahrenheit. 

The  manner  in  which  I  secured  the  eggs  for  study  was  simple  enough.  Several  shallow 
glass  dishes  were  prepared  by  painting  the  bottoms  black.  Having  dredged  a  lot  of  speci- 
mens, I  arranged  them  in  a  circle  around  the  edges  of  the  dish,  with  their  anterior  ends 
pointing  toward  the  centre  of  the  dish.  By  arranging  the  specimens  in  this  manner  the 
difference  in  the  sexes  becomes  at  once  apparent. 

The  eggs  are  discharged  from  the  anterior  margin  and  drop  just  beyond  the  pallial  mem- 
brane, hanging  in  clusters  from  the  setae,  and  covering  the  bottom  of  the  dish  in  the  imme- 
diate vicinity  of  the  animal,  presenting  the  appearance  of  a  white  powder,  though  with  a 
simple  lens  thfc  individual  eggs  are  plainly  seen.  They  are  opaque  and  spermaceti  white  in 

MEMOIRS  BOST.  SOC.  NAT.  HIST.     VOL.  II  64 


254  EMBRYOLOGY  OF  TEREBRATULINA. 

color.  In  the  course  of  a  few  hours  they  become  clothed  with  cilia,  and  while  many 
of  them  slowly  move  away,  some  remain  and  perish,  or,  at  least,  show  no  sign  of  devel- 
opment. These  are  probably  not  fertilized. 

The  sexes  are  separate,  and  the  spermatozoa  are  discharged  by  the  males  in  the  same 
way  that  the  eggs  are  discharged  by  the  female,  but  whether  the  eggs  are  fertilized  after 
they  have  left  the  parent,  or  before,  I  was  not  able  to  determine,  as  different  lots  of  eggs 
behaved  differently  after  their  escape.  In  some  cases  the  eggs  did  not  appear  to  be  locomo- 
tive until  two  or  three  days  after  their  discharge,  while  in  other  cases  they  became  active 
on  the  day  of  their  discharge. 

Great  care  must  be  taken  to  change  the  water  every  day,  since  the  water  soon  becomes 
vitiated,  and  Paramjecia  rapidly  develope  and  appear  to  feed  upon  the  embryos.  The  tem- 
perature of  the  water  must  be  kept  as  near  as  possible  to  that  from  which  they  were 
taken.  In  drawing  and  replacing  the  water  a  glass  syphon  was  found  the  best,  as  in  this 
way  the  embryos  were  not  disturbed,  though  some  skill  was  required  during  the  active 
natatory  condition  of  the  embryos,  to  prevent  them  from  leaving  the  dish  also. 

The  development  of  the  embryo  presents  a  series  of  well  defined  stages,  and  I  shall 
consider  each  stage  in  turn.  In  the  first  stage  the  embryo  becomes  widened  at  one  end. 
The  segments  are  barely  indicated,  the  .posterior  end  is  the  widest,  the  anterior  portion  is 
ornamented  with  a  conspicuous  tuft  of  long  cilia,  so  peculiar  to  the  embryos  of  many 
worms.  The  embryo  is  also  clothed  with  vibratile  cilia,  and  in  this  condition  slowly 
moves  along  the  bottom  of  the  dish  without  rising  from  it,  or  remains  quiet.  In  the  sec- 
ond well  marked  stage  the  embryo  is  divided  into  two  prominent  segments,  these  expand 
and  contract  upon  each  other  slightly,  and  the  cephalic  segment  has  the  power  of  partially 
bending  from  side  to  side.  In  this  stage  the  embryo  is  most  active,  swimming  rapidly  in 
every  direction  and  turning  abruptly  about.  The  oesophagus  also  becomes  dimly  denned. 
In  the  third  stage  the  peduncular  segment  is  developed  and  projects  from  the  posterior 
portion  of  what  can  now  be  called  the  thoracic  segment.  At  this  stage  the  embryo  either 
remains  immovable  upon  the  bottom  of  the  dish  or  slowly  moves  about.  In  two  cases  deli- 
cately barbed  seta?  to  the  number  of  thirty-five  projected  directly  backward  from  the  pedun- 
cular segment.  In  the  fourth  stage  the  embryo  becomes  attached  by  means  of  its  peduncular 
segment.  The  embryo  is  still  clothed  with  cilia,  though  the  long  pencil  of  cilia  has  disap- 
peared. The  head  is  closely  drawn  to  the  thoracic  segment,  which  becomes  wider  in  trans- 
verse diameter,  so  as  nearly  to  hide  the  peduncle.  In  the  fifth  stage  the  thoracic  ring 
commences  to  fold,  or  turn  upward  upon  opposite  surfaces  of  its  circumference,  so  as  to 
gradually  enclose  the  head ;  one  fold  being  made  slightly  in  advance  of  the  other  represents 
the  larger  or  ventral  valve.  In  this  stage  appear  clusters  of  barbed  and  deciduous  setos 
upon  the  anterior  margin,  and  in  a  later  portion  of  this  stage  the  first  hardened  areas  of 
the  dorsal  and  ventral  plates  make  their  appearance,  and  the  cirri  appear  as  blunted  papil- 
lae about  the  mouth.  In  the  sixth  stage  the  shell  becomes  rounded,  the  peculiar  scaled 
structure  makes  its  appearance,  and  the  formation  of  tubules  perforatiiig  the  shell,  and  per- 
manent setae  takes  place. 

In  another  memoir  I  hope  to  present  the  characters  of  the  genitalia  of  the  Brachio- 
poda.  I  will  state  here,  however,  that  the  eggs  not  only  fill  the  large  pallial  sinuses,  but 
hang  in  clusters  from  the  genital  band ;  from  these  parts  they  escape  by  dehiscence,  and 
float  freely  in  the  perivisceral  cavity.  The  anterior  perivisceral  wall  is  sufficiently  trans- 


EMBRYOLOGY  OF  TEREBRATTJLESTA.  255 

parent  to  allow  one  to  watch  the  eggs  as  they  are  gradually  drawn  to  the  infundibulifbrm 
orifices  of  the  oviducts,  and  to  secure  them  as  they  escape  by  the  external  orifice  of  the 
oviduct.  In  parting  the  shells  for  this  purpose  great  care  must  be  taken  not  to  open  them 
too  far,  as  the  parietal  wall  will  rupture,  and  from  this  opening  the  perivisceral  fluid  and 
eggs  will  escape.  The  eggs  are  not  uniform  either  in  shape  or  size,  though  a  distinct  gran- 
ulated membrane,  the  ovishell,  is  formed  while  the  egg  is  contained  in  the  perivisceral  cav- 
ity. Segmentation  is  next  seen,  first  as  a  few  indentations  upon  the  periphery  of  the  egg, 
until  finally  the  whole  egg  presents  a  mass  of  cells,  as  shown  in  Fig.  11.  The  egg  next  as- 
sumes an  oval  shape,  becomes  ciliated,  and  in  several  eggs  at  this  stage  a  dim  opening  ex- 
tending to  the  centre  midway  between  the  opposite  poles  of  the  egg  was  seen  —  whether 
this  was  the  micropyle  or  the  scar  from  which  the  egg  escaped  from  the  ovisac  I  could  not 
determine ;  gradually  the  egg  becomes  widened  at  one  end,  which  is  to  be  the  base,  or  pos- 
terior pole  of  the  embryo.  A  long  pencil  of  cilia  springs  from  the  smaller  anterior  end,  so 
characteristic  of  the  Annelid  embryo. 

First  Stage.  From  some  of  my  drawings  it  would  seem  as  if  the  peduncular  ring  con- 
sisted of  the  primary  posterior  pole  of  the  egg,  the  thoracic  ring  widening  and  enclosing 
it.  At  all  events  the  thoracic  ring  forms  the  widest  portion  of  the  embryo,  directly  in 
front  of  which  a  second  fold  makes  its  appearance.  Whether  this  is  an  indication  of  another 
ring  I  could  not  make  out ;  later,  however,  it  merges  into  the  base  of  what  is  to  be  the 
cephalic  ring,  and  the  deep  constriction  that  is  soon  to  follow  occurs  between  this  fold  and 
the  thoracic  ring.  An  end  view  shows  the  thoracic  ring  slightly  flattened  while  the  cephalic 
ring  preserves  its  circular  outline.  In  this  condition  the  embryo  swims  slowly  about.  This 
ends  the  first  stage. 

Second  Stage.  In  this  stage,  and  one  that  seemed  of  the  longest  duration,  a  matter  of 
three  or  four  days,  the  embryo  is  quite  elongated,  and  is  divided  by  a  deep,  transverse  line 
into  two  unequal  halves,  the  head  segment  being  the  smallest.  At  this  stage  it  is  the 
most  active,  no  longer  moving  slowly  along  the  bottom  of  the  dish,  or  remaining  motion- 
less, but  ceaselessly  swimming  in  a  rapid  manner  back  and  forth  through  the  water,  and 
abruptly  turning  about ;  the  segments  expanding  and  contracting  upon  each  other,  and 
the  head  bending  from  side  to  side,  the  thoracic  segment  often  being  transversely  wrinkled 
by  this  bending.  A  peculiarity  of  the  embryo  at  this  stage  consists  in  the  various  external 
outlines  assumed  by  the  embryo,  presenting  also  different  proportions,  as  shown  in  Figs.  18, 
19,  20  and  21,  drawn  from  the  same  embryo.  The  first  definite  trace  of  internal  structure 
now  occurs  in  the  formation  of  the  alimentary  tract,  appearing  as  a  long,  narrow  tract  run- 
ning from  the  thoracic  to  the  cephalic  ring,  closed  posteriorly,  but  blending  with  the  cell 
contents  of  the  cephalic  segment.  A  clear  interspace  is  also  seen  at  the  anterior  portion 
of  the  thoracic  ring.  What  appeared  to  be  an  opening  in  the  posterior  end  of  the  embryo 
was  seen  in  some  cases. 

During  all  these  stages,  from  the  egg  upward,  great  difficulty  arises  in  making  out  any 
feature  of  internal  structure,  owing  not  only  to  the  minute  size  of  the  objects,  but  to  their 
opacity,  and  what  little  has  been  made  out  has  in  most  cases  been  done  by  slightly 
compressing  the  embryo. 

During  this  active  swimming  stage  in  some  embryos  is  seen  a  structure  that  appears  to 
be  the  incipient  peduncular  segment.  In  Plate  viu.,  Fig.  25,  and  Plate  ix.,  Fig.  78,  a  rounded 
process  is  seen  protruding  from  the  thoracic  segment,  the  walls  of  which  extend  as  far  as 


256  EMBRYOLOGY  OF  TEREBRATULINA. 

the  division  between  the  two  segments.  The  alimentary  tract  is  seen  here,  its  anterior  por- 
tion blending  with  the  cell  contents  of  the  cephalic  ring,  while  posteriorly  it  hangs  in  the 
cavity  supposed  to  be  the  incipient  peduncular  segment.  Whether  this  is  the  proper  inter- 
pretation I  cannot  say,  and  the  difficulty  arises  from  the  fact  that  in  some  embryos  farther 
advanced  this  structure  does  not  appear.  Thus  in  Fig.  83,  Plate  ix.,  an  embryo  is  shown  in 
which  no  sign  of  the  peduncle  appears,  and  yet  it  seems  in  advance  of  the  one  just 
described,  in  showing  the  widening  of  the  thoracic  ring,  one  side  of  which  shows  a  bulging 
which  represents  the  future  ventral  fold.  An  irregular  cavity  is  thus  left  by  the  bulging 
of  the  external  wall,  and  in  this  cavity  at  a  later  stage  I  have  seen  the  circulation  of 
minute  granules.  Within  this  cavity  is  another  cavity  bordered  by  thick  walls  which  hang 
from  the  suture  dividing  the  two  segments.  The  alimentary  tract  is  seen  suspended  between 
the  two  segments,  and  showing  a  faint  connection  with  this  cavity.  The  cephalic  segment 
shows  no  change  in  its  granular  contents  save  the  presence  of  the  alimentary  tract. 
The  parts  surrounding  this  tract  are  continually  contracting  in  a  spasmodic  way,  though  no 
trace  of  a  muscular  band  could  be  detected.  The  interpretation  of  these  cavities  has  per- 
plexed me  exceedingly.  The  most  reasonable  supposition  is  that  the  outside  cavity  in  the 
thoracic  ring  marked  pi.  represents  the  cavity  from  which  the  pallial  sinuses  are  to  arise ;  in 
this  cavity  I  observed  the  circulation  of  minute  granules,  as  before  stated.  The  cavity 
within  surrounded  by  thick  walls  is  the  peduncular  cavity,  and  a  faint  interspace  running 
from  the  upper  part  of  this  cavity  to  the  base  of  the  digestive  tract  appears  to  be  the  open- 
ing up  of  the  peduncular  cavity  into  the  cephalic  segment,  a  cavity  in  which  the  stomach  is 
afterwards  to  be  suspended,  and  this  may  be  called  the  perivisceral  cavity.  In  Lingula  and 
Discina  the  peduncular  and  perivisceral  cavities  are  in  open  communication.  In  Discina  the 
large  azygos  opening  is  very  apparent.  Future  study  will  undoubtedly  modify  the  inter- 
pretation of  these  cavities,  and  possibly  show  it  to  be  altogether  wrong. 

In  the  hundreds  of  embryos  examined,  a  few  only  were  of  sufficient  transparency  to  re- 
veal any  structure  within,  and  from  this  stage  onward,  the  difficulty  in  this  respect  increases, 
as  the  embryo  becomes  more  opaque,  and  with  the  after  formation  of  the  dorsal  and  ventral 
plates,  combined  with  their  minute  size,  render  the  study  of  their  internal  structure  almost 
hopeless.  Plate  ix.,  Fig.  86,  represents  the  peduncular  portion  just  ready  to  protrude. 

Third  Stage.  In  this  stage  the  peduncular  segment  has  made  its  appearance  as  a 
rounded  knob,  varying  in  size  in  different  embryos.  Soon  after  the  appearance  of  the 
peduncle,  granules  are  seen  gathering  about  its  end,  apparently  adhering  to  the  mucus 
secreted  by  it.  Soon  afterward  adhesion  takes  place,  the  embryo  remaining  fixed  when  the 
water  is  disturbed,  though  even  before  the  embryo  becomes  attached,  the  bulging  of  the 
thoracic  ring  becomes  more  conspicuous,  leaving  a  clear  cavity  within.  The  walls  of  this 
bulging  portion  present  a  number  of  highly  refractive  granules  scattered  evenly  over  its 
surface.  This  portion  first  loses  its  cilia  (Plate  ix.,  Fig.  87)  just  before  attachment ;  the 
embryo  becomes  sluggish,  or  at  least,  in  most  cases,  ceases  to  swim  actively.  In  two  cases 
a  cluster  of  delicately  barbed  setae,  to  the  number  of  'thirty-five,  was  seen  to  project 
directly  backward  from  the  posterior  end  (Plate  ix.,  Fig.  79).  That  these  were  very  tran- 
sient is  evident  from  the  fact  that  they  were  only  observed  in  two  cases  out  of  three  hun- 
dred and  fifty-two  different  embryos  examined.  The  head  continues  to  move  freely,  and 
shows  a  slight  fold  at  its  base.  As  the  head  contracts,  the  thoracic  ring  widens  ;  this  is  shown 
in  Plate  i.,  Figs.  42,  43,  where  the  same  is  sketched  with  the  segments  extended  and 


EMBRYOLOGY  OF  TEREBRATULIXA.  257 

contracted.  In  many  embryos  the  thoracic  ring  presents  an  indentation  on  one  side,  as  if 
the  ring  were  a  band  partially  uniting  at  this  place.  The  peduncle  gradually  widens  at  the 
end  into  a  sucking  disk,  and  at  this  time  the  embryo  becomes  permanently  attached. 

Fourth  Stage.  The  embryo  now  settles  down  upon  its  base  of  attachment,  the  tho- 
racic segment  widening  and  flattening,  and  appearing  pressed  to  its  point  of  support,  so  as 
to  conceal  the  peduncle.  The  head  is  closely  pressed  to  the  thoracic  segment,  the  clear 
space  within  having  disappeared,  and  the  head  only  appearing  ciliated.  And  now  com- 
mences the  most  important  portion  of  the  developmental  history,  in  which,  for  the  first 
time,  we  become  acquainted  with  the  development  of  the  dorsal  and  ventral  plates. 

Fifth  Stage.  The  thoracic  segment  commences  to  fold  upon  both  sides  of  the  head,  and 
these  are  the  dorsal  and  ventral  folds.  Gradually  the  head  is  enclosed  by  the  folds.  In  this 
portion  of  their  history  I  was  peculiarly  fortunate  in  securing  hundreds  of  examples  just 
after  they  had  become  attached  to  adult  Terebratulina.  These  I  studied  in  their  natural 
positions.  In  some  cases  the  Terebratulina  had  been  torn  from  Mytilus,  to  which  they  had 
been  attached.  The  peduncular  disk  brought  away  a  layer  of  the  black  epidermis  of  the 
Mytilus,  and  to  this  surface  many  embryos  conveniently  became  attached,  and  against  this 
black  background  the  pure  white  embryo  showed  to  the  best  advantage.  At  intervals  the 
Terebratulina  would  twirl  its  peduncle,  thus  presenting  the  embryos  in  different  positions,  all 
of  which  I  instantly  sketched.  I  have  a  great  many  drawings  at  every  stage  of  this 
interesting  growth,  some  of  which  are  given  on  Plate  vni.,  Figs.  47  to  77,  inclusive. 

One  fold  grows  more  rapidly  than  the  other,  and  I  infer  that  this  is  to  be  the  larger  or 
ventral  plate.  The  head  appears  to  be  gradually  engulfed,  as  it  were,  though  for  a  long 
time  protruding  beyond  the  dorsal  and  ventral  folds.  The  folds  also  present  for  a  long 
time  a  thickened  and  rounded  border.  The  inner  edge  of  what  I  suppose  to  be  the  dorsal 
valve,  shows  a  distinct  notch  in  the  median  line  in  some  (Plate  vin.,  Fig.  63).  As  the  dor- 
sal and  ventral  folds  develop,  the  embryo  becomes  elevated  upon  the  peduncular  stalk,  and 
the  attachment  becomes  so  firm  that  a  forcible  stream  of  water  falling  upon  them  does  not 
detach  them,  indeed  a  point  of  a  needle,  or  a  stiff  camel's  hair  pencil,  was  found  necessary 
for  the  purpose,  and  in  the  removal,  the  parts  were  so  soft  as  to  break  down  in  most  cases. 
The  mouth  also  makes  its  appearance  at  this  time,  the  head  for  a  long  time  occupying  the 
area  enclosed  by  the  two  folds.  As  soon  as  the  embryo  rises  upon  its  peduncle  it  drops 
partially  over  to  one  side,  the  ventral  or  larger  area  being  uppermost. 

The  hinge  margin  is  broad  and  slightly  rounded  when  looked  at  from  above ;  a  side  view, 
however,  presents  a  wide  and  flattened  area,  as  is  shown  in  some  species  of  Spirifer,  and 
the  embryo  for  a  long  time  assumes  the  position  that  the  Spirifer  must  have  assumed.  The 
dorsal  and  ventral  folds  close  up  on  the  sides,  and  their  edges  become  sharper  ;  the  future 
lateral  openings  of  the  shell  gradually  extend  to  the  base.  From  above,  the  thorax  is  wider 
than  long.  Starting  from  a  broad  base  it  widens  gradually  to  the  anterior  margin,  which  is 
nearly  straight,  to  which  it  joins  by  a  short  curve.  A  heart-shaped  corneous  shell  is  formed 
even  at  this  early  stage,  for  in  several  cases  I  met  with  it  where  the  softer  portions  had 
been  removed  by  Paramaecia.  (See  Plate  vin.,  Fig.  68.) 

Before  the  folds  have  closed  over  the  head,  four  bundles  of  setae  appear ;  one  bundle 
containing  from  seven  to  nine  setae  springing  from  where  the  folds  unite  laterally.  These 
stand  out  at  nearly  right  angles  to  the  longitudinal  axis.  The  other  bundles  containing 
from  two  to  four  setae,  spring  from  a  point  midway  between  the  first  bundles  and  the 

MEMOIRS  HOST.   SOO.  NAT.   HIST.     VOL.   II.  65 


258  EMBRYOLOGY  OF  TEREBRATULINA. 

median  line  anterior.  Thus  the  embryo  possesses  from  twenty  to  twenty-five  setoa  spring- 
ing from  the  anterior  margin.  The  larger  and  lateral  bundles  of  setae  are  the  first  to  make 
their  appearance.  They  are  nearly  as  long  as  the  entire  length  of  the  embryo,  and  are  deli- 
cately barbed  and  deciduous.  Upon  pressure  of  the  embryo  they  readily  separate  from 
their  base  of  attachment.  The  dorsal  valve  is  flattened,  while  the  ventral  valve  is  rounded, 
as  before  remarked.  The  first  evidence  of  hardened  plates  appears  in  the  later  stages  of 
these  forms,  for  upon  crushing  the  embryo  in  the  live  cage  a  number  of  angular  fractures 
appear.  (Plate  n.,  Figs.  89  and  91.) 

Fig.  85,  Plate  II.,  presents  a  view  of  an  advanced  stage,  in  which  the  relative  position 
and  character  of  the  deciduous  setae  are  shown. 

Fig.  81,  just  above,  represents  the  same  embryo  as  it  appeared  when  slightly  crushed. 
The  manner  in  which  the  contents  burst  out  from  the  shell  still  held  by  the  membrane,  as 
in  a  sac,  the  fracture  of  the  shell  and  the  detached  setaa,  are  all  instructive.  Besides  the 
minute  granules  which  make  up  the  substance  of  the  embryo,  larger  cells,  to  the  number 
of  twenty-five  or  more,  are  seen  scattered  through  the  mass.  In  a  slightly  advanced 
stage,  Fig.  90,  Plate  II.,  the  mouth  shows  on  each  side  a  rounded  papilla,  the  first 
appearance  of  the  cirri.  The  mouth  is  prominent,  and  flush  with  the  anterior  borders  of 
the  pallial  membrane ;  this  is  also  shown  in  Fig.  82. 

Fig.  91  represents  the  appearance  of  Fig.  90  crushed.  Here  the  incipient  cirri  show  as 
two  prominences,  one  upon  each  side  of  the  mouth.  The  shell  fracture  is  also  more  appar- 
ent. As  the  embryo  advances  in  growth  the  outline  changes,  having  at  first  a  transversely 
semicircular  outline  with  the  posterior  margin  straight,  as  in  Leptaena.  It  gradually  elongates, 
and  commences  to  widen  its  anterior  margin,  as  in  Fig.  93  ;  it  becomes  well  rounded  as  in 
Fig.  88,  and  at  this  tune  is  seen  a  difference  in  the  length  of  the  dorsal  and  ventral  plate, 
and  for  the  first  time  appear  concentric  lines  of  growth:  The  deciduous  seise,  at  this  stage, 
separate  at  the  slightest  handling  of  the  embryo,  and  as  in  every  case  the  figures  on  the 
plates  are  exact  fac-similes  of  my  original  drawings,  the  setae  are  not  shown  in  Fig.  88, 
as  they  dropped  off  in  removing  the  specimen  to  the  live  box.  A  stage  of  the  same  age, 
or  slightly  later,  is  shown  in  Fig.  94,  and  this  stage  immediately  precedes  the  formation 
of  the  scaled  structure  of  the  shell.  Its  outline  is  quite  unlike  any  adult  Brachiopod 
known.  It  is  longer  than  broad.  The  posterior  margin  is  quite  broad  and  rounded.  The 
anterior  margin  is  twice  the  breadth  of  the  hinder  margin,  semicircular,  and  abruptly 
rounded  where  it  meets  the  lateral  margins,  which  are  incurved.  The  larger  bundles  of 
setaa  project  at  the  point  where  the  anterior  curved  margin  joins  the  lateral  margin.  (See 
Fig.  94.)  A  distinct  triangular  area  is  seen  within,  which  represents  the  head,  below  which 
the  digestive  tract  is  faintly  indicated. 

Sixth  Stage.  The  embryo  has  now  discarded  its  deciduous  setae,  and  for  the  first  time 
the  permanent  setae  make  their  appearance,  as  well  as  the  peculiar  scaled  structure  of 
the  calcareous  shell,  and  with  these  new  features  that  of  the  peculiar  tubules  perforating 
the  shell  must  be  added. 

Fig.  96  represents  a  somewhat  more  advanced  stage  than  Fig.  94.  The  form  is  now 
bluntly  oval,  its  posterior  margin  prominent  and  bluntly  rounded.  In  general  contour  it 
recalls  Siphonotreta,  placed  in  the  family  Discinidaa  by  Davidson,  a  genus  not  occurring 
above  the  Silurian.  Seven  prominent  seta?  longer  than  the  shell  now  spring  and  diverge 
from  the  anterior  margin.  These  are  not  barbed.  The  shell  now  plainly  shows  its  scaled 


EMBRYOLOGY  OF  TEREBRATULIXA.  259 

structure,  and  within  is  seen  four  cirri,  below  which  the  digestive  cavity  occurs.  The  tubules 
first  formed  are  three  in  number,  of  large  size,  and  are  arranged  in  a  triangular  figure,  the 
two  forming  the  base  of  the  triangle  occurring  midway  between  the  front  and  hinder  por- 
tions of  the  head,  the  other  tubule  being  near  the  anterior  margin. 

The  tubules,  or  pores  first  formed,  present  some  new  and  interesting  features.  In  every 
case  examined,  the  first  that  make  their  appearance  are  three  in  number,  and  are  invariably 
arranged  so  as  to  form  a  triangle  as  shown  in  Figures  95,  96  and  105.  They  are  also  much 
larger  than  those  subsequently  formed.  They  are  oval  in  shape,  and  within  their  borders  a 
circular,  granulated  plug  of  a  reddish  yellow  color  is  seen,  between  which  and  the  outer 
border  of  the  tubule  a  clear  space  is  visible.  From  twelve  to  fourteen  hairs  of  various 
lengths,  some  of  them  three  times  as  long  as  the  diameter  of  the  pore,  spring  from  the 
margin  of  the  granulated  disk,  and  radiate  in  every  direction.  That  these  are  veritable 
hairs  and  not  minute  tubules  in  the  shell,  or  any  internal  markings,  I  proved  in  a  very  sim- 
ple manner.  First  I  made  an  exceedingly  careful  drawing  of  the  tubule,  showing  exactly 
the  position  of  each  hair,  and  then  brushing  the  pores  slightly  with  a  delicate  camel's  hair 
pencil  I  again  made  a  careful  drawing  of  the  same  pores,  using  the  same  objective,  |  Wales. 
The  hairs  were  found  in  every  case  to  have  changed  positions,  being  bent  in  different  direc- 
tions. Fig.  100,  a,  represents  a  drawing  of  the  tubule  before  brushing,  though  in  this  the 
hairs  were  bent  in  handling  the  specimen,  and  Fig.  100,  &,  represents  the  same  pore  after 
brushing.  Next  summer  I  hope  to  study  this  peculiar  structure  of  the  tubule  with  higher 
powers.  The  tubules  subsequently  formed  are  much  smaller  in  size,  showing,  however,  the 
same  hairs  in  less  number  radiating  from  them. 

Whether  there  is  any  relation  between  these  veritable  hairs  and  the  radiating  lines  sur- 
rounding the  tubules,  as  described  by  Queckett  and  Carpenter,  and  regarded  by  them  at  one 
time  as  representing  cilia,  I  cannot  «ay.  In  this  connection,  however,  it  is  interesting  to 
recall  other  views  on  the  subject.1  It  is  more  probable  that  the  tubules  are  simply  organs 
of  general  sensibih'ty.  In  the  test  of  Crustacea  similar  tubules  occur,  which  penetrate  to 
the  vascular  layer  beneath,  and  are  regarded  as  endowing  the  test  with  a  general  sensi- 
bility.2 The  subsequent  tubules  appear  to  make  their  appearance  in  a  certain  symmetrical 
order  as  shown  in  Fig.  105,  one  occurring  on  each  side  of  the  peduncle.  In  Fig.  102  a  dis- 
tinct area  is  seen,  from  the  anterior  surface  of  which  the  cirri  spring,  and  from  the  borders 
of  which  the  scaled  structure  of  the  calcareous  shell  commences  to  form  This  area  has  the 
same  outline  as  the  stage  represented  in  Fig.  94.  The  cirri  present  coarse  cilia  as  long  as 
the  diameter  of  the  cirrus ;  the  cavity  within  is  large,  on  the  outer  border  of  which  a  few 
irregular  granules  are  arranged  in  a  single  line.  See  Fig.  101,  representing  a  cirrus  from 
stage  102. 

This  brings  the  development  of  Terebratulina  up  to  its  "  Early  Stages,"  already  de- 
scribed by  me  in  these  Memoirs.3 

By  comparing  the  early  conditions  of  the  embryo  Terebratulina  with  that  of  Thecidium, 
described  by  Lacaze-Duthiers,  a  certain  resemblance  is  observed,  so  far  as  the  division  of 

1  See  an  interesting  paper  of  Prof.  King  on  the  structure  Hairs  of  Crustacea,  Philosophical  Transactions,  Vol.  CXLVIII, 

of  the  tubules  in  the  test  of  Brachiopoda,  in  the  Memoirs  of  p.  805. 
the  Royal  Irish  Academy,  Vol.  xxiv,  p.  439.  8  Morse.     Early  Stages  of   Terebratulina.      Mem.  B.   S. 

3  See  De  Morgan  on  the  Structure  and  Functions  of  the  N.  II.,  Vol.  n.,  p  29. 


2GO  EMBRYOLOGY  OF  TEREBRATULINA. 

the  body  into  segments,  and  their  power  of  contracting  upon  each  other  is  concerned, 
though  the  conditions  under  which  they  develop  will  be  found  to  be  entirely  unlike.  The 
egg  of  Terebratulina  is  discarded  freely  into  the  water  to  undergo  its  development,  and 
possibly  its  fertilization  outside  the  parent,  while  the  embryo  Thecidium  is  held  attached 
within  the  pallial  cavity,  and  separates  only  after  it  has  undergone  changes  in  advance  of 
those  found  in  the  embryo  Terebratulina  after  it  has  become  permanently  attached. 

The  presence  of  eye  spots  in  the  embryo  Thecidium  is  another  important  difference,  for 
though  I  examined  hundreds  of  the  Terebratulina  embryos,  yet  in  no  instance  were  the 
traces  of  eye  spots  detected.  On  comparing  the  early  stages  of  Terebratulina  with  that  of 
Discina,  we  are  at  once  struck  by  the  marked  differences  between  the  two ;  Terebratulina 
becoming  permanently  attached  by  its  peduncular  segment  long  before  a  trace  of  the  pecu- 
liar dorsal  and  ventral  plates  makes  its  appearance,  or  even  before  any  definite  structure 
shows  within,  while  Discina  swims  freely  in  the  water  sometime  after  the  dorsal  and  ven- 
tral plates,  cirri,  mouth,  oesophagus  and  stomach,  have  made  their  appearance. 

The  long  and  protrusible  oesophagus  and  head,  bearing  a  crown  of  eight  cirri,  or  tenta- 
cles, in  Discina,  as  described  by  Dr.  M  tiller,  is  unlike  anything  of  the  kind  observed  in 
Terebratulina.  Their  barbed  and  deciduous  setas,  however,  present  similar  features  to  those 
of  the  embryo  Terebratulina. 

The  embryology  of  Lingula  (which  I  hope  soon  to  have  the  opportunity  of  studying  on 
the  coast  of  North  Carolina)  will  undoubtedly  afford  stages  similar  to  those  observed  in  Dis- 
cina. I  have  already  studied,  in  the  transparent  plates  of  Lingula  pyramidata,  the  charac- 
ter of  the  nucleus,  and  find  it  perfectly  orbicular  with  a  margin  finely  notched,  and  in  cer- 
tain fossil  LingulaD  I  have  observed  the  same  orbicular  nucleus.  With  the  other  characters, 
in  common  between  Lingula  and  Discina,  we  should  expect  to  find  similar  features  revealed 
in  their  embryology. 

In  considering  the  various  degrees  of  persistence  of  embryonic  features  in  the  few  forms 
we  are  thus  far  acquainted  with,  we  are  struck  with  the  great  difference  in  this  respect  be- 
tween Discina  on  the  one  hand,  and  Terebratulina  on  the  other.  Thus,  in  Discina,  attach- 
ment takes  place  sometime  after  adult  characters  make  their  appearance,  the  peduncle  at 
first  extending  directly  backward,  as  in  Lingula.  In  Lingula,  as  I  have  heretofore  ob- 
served, attachment  never  takes  place,  at  least  in  L.  pyramidata,  the  creature  living  loose  in 
the  sand ;  and  this  feature  will  probably  be  found  characteristic  of  other  LingulaB  when 
they  shall  have  been  carefully  observed. 

Thus  we  see  in  later  geological  forms,  attachment  taking  place  earlier  in  developmental 
history  than  in  those  of  earlier  geological  times.  Similarly  in  earlier  geological  times  we 
find  forms  in  which  the  dorsal  and  ventral  plates  are  chitinous,  and,  as  I  have  observed  in 
Lingula  pyramidata,  of  such  transparency  that  the  circulating  fluid  could  be  easily  seen 
coursing  through  the  sinuses  of  the  pallial  membranes,  and  in  this  latter  species  containing 
so  little  earthy  matter  that  wrhen  dry  they  become  twisted  out  of  all  shape,  and  even  roll 
up  like  a  leaf.  With  these  facts  it  requires  no  hazardous  supposition  to  conceive  the  pri- 
mordial Brachiopods  devoid  of  the  dorsal  and  ventral  plates,  or  furnished  only  with  a  semi- 
lunar  membrane  on  the  head,  as  in  that  curious  annelid  Umbellisyllis,  described  by  Sars, 
and  of  a  form  that  presented  the  annelidan  characters  less  disguised  by  features  that  have 
heretofore  prevented  a  right  conception  of  their  affinities. 

As  to  the  relations  of  the  Brachiopods  with  the  Polyzoa,  some  features  of  similarity  are 


EMBRYOLOGY  OF  TEREBRATULINA.  261 

seen  between  the  embryo  Brachiopod  and  the  free  embryo  of  Pedicellina,  described  by  Van 
Beneden,1  though  the  development  of  parts  within  a  ccenoecium,  and  the  formation  of  stat- 
oblasts  are  features  quite  unlike  the  Brachiopod.  A  roundabout  relation  might  possibly  be 
insisted  upon  through  the  Rotifera,  in  their  winter  ova. 


After  this  paper  had  been  made  up  into  pages,  Mr.  Alex.  Agassiz  called  my  attention  to 
the  fact  that  Prof.  John  McCrady  had  published  in  the  Proceedings  of  the  Elliott  Society  of 
Natural  History  of  Charleston,  S.  C.,  a  notice  of  a  larval  Brachiopod. 

After  a  fruitless  search  among  the  libraries  of  Boston  for  a  perfect  set  of  the  Proceedings 
of  this  Society,  I  learned  that  within  a  week  Mr.  McCrady  had  made  his  home  in  Cambridge, 
having  recently  become  connected  with  the  Museum  of  Comparative  Zoology.  From  him 
I  learned  that  the  original  description  and  drawing  was  presented  before  the  Elliott  Society, 
at  its  meeting  June  15th,  1860,  but,  owing  to  the  war,  had  never  been  published  by  the 
Society.  In  the  destruction  of  Columbia,  S.  C.,  by  Sherman's  Army,  Prof.  McCrady  not 
only  lost  his  valuable  library,  but  all  of  his  scientific  records,  drawings  and  notes.  After  this 
irreparable  loss,  he  drew  up  from  memory  a  description  of  this  Brachiopodan  larva,  and 
now  generously  allows  me  to  make  free  use  of  this  valuable  manuscript,,  which  contains  the 
first  and  only  observations  on  a  larval  Lingula  ever  made. 

The  creature  in  question  was  found  by  him  either  late  in  the  fall  of  1859,  or  in  the 
spring  of  1860,  he  cannot  now  remember  which.  It  was  found  off  Sullivan's  Island 
in  Charleston  Harbor.  The  following  is  quoted  from  his  manuscript. 

"  1st.     The  larva  is  a  free  swimming  animal. 

"  2d.  Its  means  of  locomotion  are  large  vibratile  cilia,  clothing  the  cirri  of  the  arms, 
precisely  as  in  Bryozoa. 

"  3d.  It  was  provided  with  a  bivalve  semi-transparent  horny  shell,  recalling  the  shell  of 
Lingula,  but  with  no  trace  of  a  foot  stalk."  (Mr.  McCrady  adds  hi  pencil  that  the  form  of 
the  shell  was  flattened,  and  more  ventricose  than  that  of  adult  Lingula.) 

"  4th.  In  motion  the  valves  were  opened  just  enough  to  allow  free  play  to  the  ciliated 
cirri  of  the  arms,  which  (i.  e.,  the  cirri)  was  thrust  out  beyond  the  shell  rim. 

"  5th.  The  arms  were  never  extended  beyond  the  shell  rim,  but  just  within  and  along 
their  margin. 

"  6th.  The  opacity  of  the  body  was  such,  that  added  to  the  cloudy  semi-transparency  of 
the  horny  shell,  it  was  impossible  to  make  out  other  details. 

"  7th.  When  the  larva  ceased  swimming,  the  arms  and  their  cirri  were  retracted,  the 
valves  closed,  and  the  animal  sank  to  the  bottom." 

By  comparing  the  above  description  with  that  of  Dr.  Fritz  Miiller's  description,  given  in 
the  first  part  of  this  memoir,  the  closest  similarity  will  be  observed  between  them  in  their 
general  appearance,  their  mode  of  swimming,  and  even  to  the  manner  in  which,  when  at 
rest,  they  close  their  shells  and  sink  to  the  bottom  of  the  vessel  in  which  they  are  confined. 
Mr.  MpCrady  assures  me  he  has  never  seen  Miiller's  description  of  the  larval  Discina. 

It  is  interesting  to  remark  that  nearly  at  the  same  time,  these  two  naturalists  should  make 
the  first  observations  ever  made  on  the  embryology  of  the  Brachiopods,  if  we  except  the 
very  brief  notice  of  Oscar  Schmidt. 

1  Hist.  Nat.  du  genre  Pedicellina.     Mem.  AcaVl.  Royal  de  Belgique.     Tome  xix. 

MKMOIR9   B09T.   8OC.  XAT.   HIST.     VOL.  II.  66 


262  EMBRYOLOGY  OF  TEREBRATULINA. 

The  expression  of  mine  which  occurs  above,  that  the  embryology  of  Lingula  when 
known  would  agree  with  that  of  Discina,  was  in  type  long  before  I  became  aware  of  Mr. 
M°Crady's  discovery. 

The  absence  of  setas  in  the  embryo,  with  the  opacity  of  the  valves,  is  an  evidence  that  it 
was  considerably  advanced,  for  Muller  described  some  of  the  larva  observed  by  him  as  hav- 
ing lost  the  larger  bristles. 

In  closing  this  brief  memoir  I  wish  to  express  my  thanks  to  Mr.  Richard  Rathbun,  who 
accompanied  me  to  Eastport,  and  who  assisted  me  in  securing  materials  for  study. 

To  Mr.  Edward  Burgess  I  am  again  under  many  obligations  during  the  preparation  of 
the  paper. 

My  thanks  are  also  due  to  Mr.  Chas.  A.  Walker,  who  has  with  great  fidelity  and  patience 
reproduced  accurately  my  drawings  upon  steel. 


EXPLANATION  OF  PLATES. 
PLATE  VIII. 

Fig.  1.    A  cluster  of  eggs  from  the  genital  band. 

Fig.  2.    A  single  egg  encased  in  its  capsule. 

Figs.  3,  4,  5.    Eggs  from  the  peri  visceral  cavity  immediately  after  their  escape  from  the  pallij.1  sinuses. 

Fig.  6.    Highly  magnified  portion  of  the  eggshell. 

Figs.  7,  8,  9,  10  11.    Eggs  in  various  stages  of  segmentation. 

Fig.  12.    First  ciliated  stage. 

Figs.  13,  14,  15,  16,  17.  Successive  stages  of  transverse  division  of  embryo,  showing  long  tuft  of  cilia  at 
cephalic  extremity. 

Figs.  18,  19,  20,  21.    From  a  single  embryo,  showing  various  outlines  assumed  while  swimming. 

Figs.  22,  23,  24.    Different  views  of  another  embryo. 

Figs.  25,  26,  27.    Different  embryos  showing  first  appearance  of  caudal  or  peduncular  segment. 

Figs.  28  to  36.    Different  embryos  at  the  stage  when  the  caudal  segment  becomes  conspicuous. 

Figs.  29,  30.    Representing  the  same  embryo  contracted  and  expanded. 

Figs.  37,  38,  39,  40,  41.     Embryos  just  attaching  themselves  by  their  caudal  segment. 

Figs.  42,  43.  Drawn  from  the  same  embryo :  the  first  showing  the  embryo  stretched  to  its  utmost,  the  sec- 
ond the  same  contracted.  (These  motions  would  often  follow  each  other  rapidly.) 

Figs.  44,  45.    Embryos  showing  first  appearance  of  ventral?  area  by  the  bulging  of  the  thoracic  ring. 

Figs.  46  to  53.  Embryos  in  various  stages  showing  widening  of  thoracic  ring,  and  its  gradual  growth 
toward  enclosing  the  cephalic  ring. 

Figs.  54  to  61.  Successive  stages  of  the  embryo  showing  formation  of  dorsal  and  ventral  areas  by  the 
folding  and  growth  of  the  thoracic  ring.  In  Fig.  61  the  head  is  still  seen  projecting  from  the  dorsal  and  ven- 
tral folds  of  the  thoracic  ring. 

Figs.  62  to  77.  Succeeding  stages  of  embryos  drawn  in  various  positions.  The  deciduous  setae  appear  in 
these  stages. 

Fig.  68.    Dorsal  and  ventral  plates  of  embryo,  the  contents  having  been  removed  by  Parama3cia. 


NOTE.  The  cilia  constantly  clothing  the  embryo  have  been  purposely  omitted  except  in  a  few  cases,  to 
save  trouble  in  engraving.  On  the  first  appearance  of  the  dorsal  and  ventral  folds  of  the  thoracic  ring,  the 
cilia  disappear  from  that  region.  Figs.  18  to  77  were  drawn  with  a  -fa  objective  of  Smith  and  Beck ;  the 
embryos  measure  about  the  TJ^  inch  in  diameter. 


EMBRYOLOGY  OF  TEREBRATULINA.  263 

PLATE    IX. 

The  figures  of  embryos  upon  this  plate  ns  follows :  78,  79,  80,  81,  82,  83,  85,  86,  87,  88,  89,  90,  91,  92,  93, 
and  94  were  drawn  with  a  Wales  J  inch ;  a  few  of  them  are  shown  less  magnified  on  Plate  VIII. 

Fig.  78.     Free  swimming  embryo  showing  first  trace  of  alimentary  tract  and  peduncular  segment. 

Fig.  79.  Free  swimming  embryo  showing  deciduous  setae  projecting  behind.  This  feature  was  only 
observed  in  two  instances. 

Fig.  80.  Showing  widening  of  thoracic  segment,  depression  of  cephalic  segment,  and  first  attachment  of 
caudal  segment. 

Fig.  81.  Appearance  of  embryo  Fig.  85  after  having  been  crushed.  The  embryo  shell,  apparently  corneous, 
is  split  at  the  peduncular  end.  The  membrane  representing  the  head  and  cephalic  wall  is  bulged  out,  with 
ruptures  from  which  the  cellular  contents  of  the  body  are  escaping,  and  the  deciduous  setae  are  separated  from 
their  base  of  support. 

Fig.  82.  First  stage  in  which  the  mouth  makes  its  appearance,  and  dorsal  and  ventral  plates  become  dis- 
tinctly marked. 

Fig.  83.  Earliest  stage  in  which  definite  internal  structure  was  found.  The  peduncular  segment  character- 
ized by  thick  walls  is  seen  hanging  in  the  thoracic  or  pallial  cavity. 

Fig.  84.     Highly  magnified  drawing  of  deciduous  setae  showing  their  barbed  character. 

Fig.  85.     Showing  arrangement  of  deciduous  setae,  and  contour  of  embryonic  shell. 

Fig.  86.    Another  stage  similar  to  that  shown  in  Fig.  83. 

Fig.  87.  Showing  first  bulging  of  thoracic  ring  and  clear  interspace  within.  This  region  is  characterized 
by  large  granules  marking  its  wall,  and  in  first  losing  its  ciliary  lining.  The  bulging  probably  indicates  the 
region  of  the  larger  or  ventral  valve. 

Fig.  88.  A  stage  slightly  advanced  from  Fig.  85,  showing  change  in  outline,  the  anterior  margin  strongly 
ciliated.  The  deciduous  setae  were  easily  dislodged  at  this  stage,  and  were  often  lost  in  examination. 

Fig.  89.     A  portion  of  shell  of  Fig.  88  crushed,  showing  by  its  fracture  a  harder  consistency. 

Fig.  90.     Stage  showing  for  the  first  time  a  primary  cirrus  or  tentacle  upon  each  side  of  its  head. 

Fig.  91.    The  same  crushed,  showing  fracture  of  shell,  and  parts  forced  out  by  pressure. 

Fig.  92.     Stage  similar  to  Fig.  85. 

Fig.  93.    A  slightly  advanced  stage  from  Fig.  92,  showing  widening  of  anterior  margin. 

Fig.  94.  A  stage  slightly  advanced  from  the  preceding,  with  a  definite  structure  showing  in  the  anterior 
portion  of  shell. 

Fig.  95.     Adult  characters  now  assumed,  permanent  setae  now  showing,  and  pallial  coeca  present. 

Fig.  96.  The  youngest  stage  met  with  in  which  adult  characters  were  present.  The  permanent  setae, 
seven  in  number,  project  from  the  anterior  margin.  The  peculiar  scaled  structure  of  the  shell  is  just  appear- 
ing, and  the  primary  pallial  coeca  are  present.  Within,  the  rounded  stomach,  and  four  tentacles  are  shown. 

Fig.  97.  Head,  tentacles  and  stomach  from  an  advanced  stage.  Figured  particularly  to  show  contour  of 
parts  about  the  head. 

Fig.  98.  A  stage  considerably  advanced  from  Fig.  96,  showing  subsequent  widening  of  the  anterior  por- 
tion of  the  dorsal  and  ventral  plates. 

Fig.  99.    A  setigerous  follicle  with  its  seta. 

Fig.  100.  a.  b.  One  of  the  primary  pallial  cosca,  showing  appearance  of  fringing  hairs,  a.  Showing  the 
position  of  hairs  before  being  disturbed  by  a  brush,  and  b,  the  same  after  having  been  brushed  with  a  delicate 
camel's  hair  pencil.  These  are  from  Fig.  105. 

Fig.  101.  A  tentacle,  or  cirrus  from  Fig.  102,  showing  cavity  within,  and  arrangement  of  calcareous  parti- 
cles, an  d  relative  size  of  cilia  clothing  it. 

Fig.  102.  A  considerably  advanced  stage  drawn  to  show  relations  of  embryonic  area,  which  is  shaded. 
This  portion  corresponds  to  stage  shown  in  Fig.  94. 

Figs.  103,  104.     Showing  appearance  of  fringing  hairs  bordering  pallial  coeca. 

Fig.  105.  Advanced  stage  to  show  relative  position  and  size  of  primary  coeca  and  the  first  appearance  of 
coeca  upon  that  portion  bordering  peduncular  opening. 

In  my  Memoir  on  the  Early  Stages  of  Terebratulina,  published  by  the  Society,  I  take  up  the  develop- 
mental history  of  Terebrutulina  from  the  stage  represented  in  Fig.  105. 


264 


EMBRYOLOGY  OF  TEREBRATULINA. 


EXPLANATION   OF   LETTERS   ACCOMPANYING    THE    FIGURES. 


m,  mouth. 

ce,  cesopliagus. 

s,  stomach. 

t,  tentacles  or  cirri. 

a,  alimentary  tract. 

pi,  pallial  cavity. 

pv,  perivisceral  cavity. 

pc,  peduncular  cavity. 

c,  cephalic  segment. 

th,  thoracic  segment, 


p,  peduncular  or  caudal  segment. 

h,  head. 

ap,  anterior  parietal  wall  and  head. 

e,  area  of  embryonic  shell. 

f,  fold  of  larger,  or  ventral  area. 
pr,  primary  cceca. 

ds,  deciduous  setae. 
es,  embryonic  shell. 
x,  foreign  particles  adhering  to  peduncle. 


Memoirs 


PI  VIII 


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EDW  S  MORSE  ON  EMBRYOLOGY  OF  TEREBRATULINA 


Memoirs  Boston  Soc.Nat.His.Vol.il. 


PL  IX 


.EDW  S, MORSE  OK  EMBRYOLOGY  OK  TEREBRATULINA 


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